Go to Gamefaqs.com and look up the cheat codes for adding items to your inventory.
There is also a list of item codes for pretty much everything in the game. The hard part will be figuring out exactly which key you need.
Here, I have a list but its in Excel format. These are just the codes for keys in the game.
A Rusty Key FormID: 00024FE9
A Warlock's Luck Key FormID: 0000A076
Abandoned House Key FormID: 000034F3
Adrian Decanius' House FormID: 0001777A
Aelwin's Key FormID: 00067DD4
Agarmir's House Key FormID: 00022BB6
Agnete's Key FormID: 00029187
Agronak's Mysterious Key FormID: 00038EE9
Ahdarji 's House Key FormID: 00035989
Akaviri Fort Key FormID: 0001C17C
Alberic Litte's Key FormID: 0002921A
Aldos Othran's Key FormID: 000034E3
Algot's House Key FormID: 0001D35C
Allectus' Key FormID: 0001DA89
Alval Uvani's Key FormID: 00035982
Ancestor Moth Key FormID: 0009DAC6
Ancestor Moth Temple FormID: 00098307
Andragil's Key FormID: 0000A080
Angelie's House Key FormID: 00022BB2
Antoinetta Marie's Key FormID: 000693D9
Anvil Chapel Key FormID: 0000A261
Anvil Dungeon Key FormID: 0000A264
Arcane Univ. Enchanter's Key FormID: 00092155
Archer's Paradox Key FormID: 0000A077
Arch-Mage's Key FormID: 00005297
Aredil's House Key FormID: 00022BDF
Aren's Strange Key FormID: 00090746
Aren's Tower Key FormID: 00098308
Arkay Chapel Undercroft Key FormID: 00091ADA
Arnora's Chest Key FormID: 00093555
Arnora's Key FormID: 00035E51
Arriana Valga's Key FormID: 000242B6
Arriana Valga's Quarters Key FormID: 000C5581
Arvena Thelas' Key FormID: 0000A26A
Arvin Dalvilu's Key FormID: 0009824D
Astinia Atius' Key FormID: 00022BC3
Athram House Key FormID: 00022BB9
Ayleid Cask Key FormID: 000A6570
Baenlin's Key FormID: 00035E48
Baeralorn's Key FormID: 0000C0F4
Bantien's Key FormID: 00022BB4
Barash House Key FormID: 000513C1
Basement Key FormID: 00035E50
Baurus' Key FormID: 0001E702
Beldaburo Key FormID: 0005E182
Benirus Manor Key FormID: 00003A97
Bernadette Peneles' Key FormID: 00029185
Bit and Bridle Key FormID: 0001D1FF
Black Brugo's Key FormID: 00085960
Blackwood Co. Basement Key FormID: 00035705
Bleak Mine Key FormID: 00098251
Borba's Goods Key FormID: 000034E7
Bradon's Key FormID: 000385A4
Bradus' Key FormID: 0000A268
Bralin's Key FormID: 000034EE
Branwen and Saliith's Key FormID: 000C47B3
Bravil Castle Key FormID: 0000A073
Bravil Chapel Key FormID: 0000A078
Bravil Dungeon Key FormID: 0000A113
Brolus' Key FormID: 00035E4D
Brotch Calus' Key FormID: 00035E56
Bruma Chapel Key FormID: 00036243
Bruma Dungeon Key FormID: 00036261
Caminalda's Key FormID: 0000A95A
Canne's Key FormID: 00029184
Captain Patneim's Key FormID: 000738E0
Captain's Key FormID: 00049357
Carandial's Key FormID: 0000A07A
Casta Scribonia's Key FormID: 0002921C
Castle Anvil Interior Key FormID: 0000A263
Castle Anvil Key FormID: 0000A262
Castle Bravil Interior Key FormID: 0000A074
Castle Bruma Interior Key FormID: 00035E45
Castle Bruma Key FormID: 00035E44
Castle Leyawiin Interior Key FormID: 0003597E
Castle Leyawiin Key FormID: 0003597D
Catacombs Key FormID: 0000C585
Chanel's Key FormID: 000242B5
Charcoal Cave Key FormID: 0008BA68
Cheydinhal Bridge Inn Key FormID: 000034E6
Cheydinhal Castle FormID: 000034EB
Cheydinhal Castle Interior FormID: 000034EC
Cheydinhal Chapel Key FormID: 000034EA
Cheydinhal Dungeon Key FormID: 000055D7
Chorrol Castle Private Area FormID: 000242B2
Chorrol Chapel Undercroft Key FormID: 00029214
Chorrol Dungeon Key FormID: 0002917D
Chorrol Jail Key FormID: 0002AD2A
Cingor's Key FormID: 00035988
City-Swimmer's Key FormID: 0000A07D
Claudius Arcadia's House Key FormID: 00022BDE
Coast Guard Station Key FormID: 0003598C
Commander's Chest Key FormID: 00093485
Commerce Office Key FormID: 0004798A
Curtis' House Key FormID: 0001D5B2
Cyronin Sintav's House Key FormID: 0001781C
Dagon Shrine Key FormID: 00033910
Damian Magius' Key FormID: 000534F3
Dar Jee's Key FormID: 00035980
Dareloth's Key FormID: 000534F4
Dark Fissure Cell Key FormID: 0005BEA0
Derics' Key FormID: 00035983
Display Case Key FormID: 00049D21
Display Case Key FormID: 0008DD5F
Divine Elegance Key FormID: 0001D205
Dorian's House Key FormID: 00022BC6
Dovyn Aren's Key FormID: 000177D3
Dro'shanji's Key FormID: 0002CF34
Dul gro-Shug's Key FormID: 00017779
Dust Eater Cell Key FormID: 0006507C
Dynari Amnis' Key FormID: 00022BBF
Echo Cave Key FormID: 0001648F
Edgar's Discount Spells FormID: 00022A72
Escape Route Key FormID: 00028EDE
Estelle Renoit's Key FormID: 00029212
Eugal Belette's Key FormID: 0002921B
Falcar's Key FormID: 0002E99F
Faregyl Inn Key FormID: 0000CBDC
Fathis Ules' Key FormID: 0001781A
Feed Bag Key FormID: 00022A71
Fighters Guild Key FormID: 0002229E
Fighting Chance Key FormID: 0001D157
First Edition Key FormID: 0001D155
First Hunter's Run Key FormID: 0018D13E
Flanau Hlaalu's Key FormID: 0002917B
Fo'c's'le Key FormID: 0000BC68
Forgotten Key FormID: 00074A8F
Fort Blueblood Key FormID: 0003CD2D
Fort Grief Door Key FormID: 0001FEEE
Fort Grief Real Key FormID: 0001FEF0
Fort Ontus Key FormID: 0004ECEC
Fort Redman Key FormID: 0009D2D6
Fort Sutch Gate Key FormID: 00032665
Francois Motierre's Key FormID: 00029218
Fyre Light Cave Key FormID: 0005B47F
Gallenus Rosentia's Key FormID: 00033C71
Ganredhel's Key FormID: 000034F2
Garrus Darelliun's Key FormID: 0003C2C1
Geem Jasaiin's Key FormID: 0001EB81
Gelebourne's Key FormID: 000385A2
Gharz House Key FormID: 000034E2
Gilen Norvalo's Key FormID: 0001D35E
Glarthir's Key FormID: 0001DC48
Glarthir's Secret Key FormID: 000831BB
Gogan's House Key FormID: 00064202
Gogron gro-Bolmog's Key FormID: 0006C677
Graman's House Key FormID: 0001D35D
Grey Throat's House Key FormID: 0001DA91
Guildmaster's Key FormID: 0018D83F
Guildmaster's Key FormID: 0006E2EA
Gundalas' Key FormID: 0003598D
Gunder's Key FormID: 00029186
Gweden Basement Key FormID: 0008696D
Hackdirt Key FormID: 00028B7B
Hagaer's House Key FormID: 0001DA94
Hame Dungeon Key FormID: 00085083
Hammer and Axe Key FormID: 00035E43
Harm's Folly Key FormID: 00189D0F
Hastrel Ottus' House Key FormID: 0001D35B
Helvius Cecia's Key FormID: 00035E54
Helvo Atius' Key FormID: 00022BB0
Henantier's Key FormID: 0002CF33
Herminia Cinna's House Key FormID: 000177F2
High Fane Key FormID: 0002AF06
Honmund's Key FormID: 00035E47
Horn Cave Cellar Key FormID: 0005B609
Horn Cave Storage Key FormID: 0005BC2A
Hrol Ulfgar's Key FormID: 00098293
Ida Vlinorman's House Key FormID: 000177EE
Imbel Family Crypt Key FormID: 000152FF
Imbel House Key FormID: 0009DB17
Imperial City Lighthouse Key FormID: 0009096C
Imperial City Sewers Key FormID: 0004F61A
Imperial Palace Key FormID: 00115E05
Imperial Prison Key FormID: 00092D8A
Imperial Prison Key FormID: 000950C2
Imperial Sewer Key FormID: 00027477
Imperial Trading Company Key FormID: 000534F5
Imperial Watch Key FormID: 00015EAF
Imperial Watch Office Key FormID: 00086967
Iniel Sintav's House Key FormID: 00017775
Inventius' Key FormID: 0000A267
Irene Metric's House Key FormID: 0001777C
Iron Key FormID: 00159826
Jair's Key FormID: 000477E4
Jakben Imbel's House Key FormID: 00022BC8
Jastia Sintav's House Key FormID: 00017819
J'bari's Key FormID: 00035981
Jearl's Key FormID: 0002007F
Jeetum Ze's Room Key FormID: 000A5650
Jenseric's Cabin Key FormID: 00064615
Jenseric's House Key FormID: 0001DB08
Jensine's Merchandise FormID: 0001D201
Jesan Sextius' Key FormID: 0000A26D
Jewelry Box Key FormID: 0000A9D7
J'Ghasta's Key FormID: 00035E55
Jirolin Doran's Key FormID: 00029219
J'mhad's House Key FormID: 00022BE0
Kalthar's Key FormID: 0000CF21
Kastus Sintav's House Key FormID: 00017817
Key FormID: 0006DF2E
Key FormID: 0003EE5D
Key of Hidden Wealth FormID: 000C59A2
King and Queen Tavern Key FormID: 00022B6E
Kvatch Guard House Key FormID: 00031D31
Kvinchal's Key FormID: 000477E3
Lazare Milvan's Key FormID: 00029190
Lelles' Quality Mercandise Key FormID: 0000A25F
Leyawiin Chapel Key FormID: 00069B16
Leyawiin City Watch Key FormID: 0003597F
Leyawiin Dungeon Key FormID: 00035F8C
Leyawiin Secret Room Key FormID: 00092156
Lighthouse Cellar Key FormID: 00054031
Lighthouse Key FormID: 0000A25E
Lindai's Royal Tomb Key FormID: 000A55FC
Lirrians' Key FormID: 00035E4B
Llevana Nedaren's Key FormID: 000034E4
Loche's House Key FormID: 0000A081
Lorkmir's House Key FormID: 00017776
Lorkmir's House Key FormID: 00017833
Lost Boy's Key FormID: 000998CF
Luciana Galena's Key FormID: 0000A07F
Luronk's House Key FormID: 0001DA8F
Lyra Rosentia's Key FormID: 00035E49
Mach-Na's Key FormID: 000034E8
Mages Guild Key FormID: 0002229C
Magul House Key FormID: 000034E1
Malyani Dalvilu's Key FormID: 00098298
Marana Rian's House Key FormID: 0001DA96
Margarte's Key FormID: 00035985
Marinus Catiotus' House FormID: 000177EF
Matthias' House Key FormID: 00022BBB
Medrike's Key FormID: 0000C32A
Methredhel's House Key FormID: 0005202F
Mine Key FormID: 0000295D
Mirabelle Monet's Key FormID: 0000A265
Miscarcand Key FormID: 000C58B6
Modryn Oreyn's Key FormID: 00029220
Moranda Gate Key FormID: 00051871
Mraaj-Dar's Key FormID: 0006FDA7
Murgakh gro-Ushag's Key FormID: 0002921E
My Bravil House Key FormID: 0004ED80
My Bruma House Key FormID: 0004ED88
My Cheydinhal House Key FormID: 0004ED87
My Chorrol House Key FormID: 0004ED8A
My Imperial City House Key FormID: 0005319E
My Leyawiin House Key FormID: 0004ED86
My Skingrad House Key FormID: 0004ED89
Mystic Emporium Key FormID: 0001D1FE
NE Watch Tower Key FormID: 00053FF3
Necromancer's Moss Rock Key FormID: 0005B912
Neville's Chest Key FormID: 000852DB
Newheim's Key FormID: 0000A269
Newlands Lodge Key FormID: 000034E5
Ninedava Gate Key FormID: 00051F8D
Nivan Dalvilu's Key FormID: 0009829E
Nord Winds Key FormID: 00035E3F
Novaroma Key FormID: 00035E3E
NW Watch Tower Key FormID: 00053FF4
Oaken-Hull's Key FormID: 0000A266
Odiil Farm Key FormID: 000C89DD
Ohtimbar's Key FormID: 000034F1
Old Key FormID: 00074A8E
Ongar's Key FormID: 00035E4E
Ontus Vanin's Key FormID: 00022BBA
Ormil's Cabin Key FormID: 0000C1FE
Ormil's Cabin Key FormID: 0007BAE0
Orthe's Key FormID: 0000C329
Orum House Key FormID: 000034EF
Othrelos' House Key FormID: 000177F0
Otumeel's Key FormID: 0003598A
Pennus Mallius' House Key FormID: 0001D5B3
Plotius' Key FormID: 0003598B
Pot Hole Cell Key FormID: 0005BD64
Prison Cell Key FormID: 00023FFD
Quill-Weave's Key FormID: 0000A26B
Ra'Jahirr's Key FormID: 00035987
Ra'jhan's House Key FormID: 000177F3
Ra'jiradh's House Key FormID: 00022BC1
Ranaline's Key FormID: 0000A07E
Rasheda's Key FormID: 00029213
Raynil's Key FormID: 000385A3
Raynil's Room Key FormID: 00038449
Redas Dalvilu's Key FormID: 000982A3
Redwater Slough Key FormID: 00070248
Regner's Key FormID: 00035E53
Reman Broder's Key FormID: 00029188
Reynald Jemane's Key FormID: 0002921D
Rimalus Bruiant's Key FormID: 00029216
Rindir's Staffs Key FormID: 0001D152
Ritual Key FormID: 00033911
Riverview Key FormID: 000034F0
Ri'Zakar's Room Key FormID: 000A564F
Roderic Pierrane's Key FormID: 00017816
Roebeck Bridge Room Key FormID: 00026CD5
Ruslan's House Key FormID: 0001DA92
Rusty Key FormID: 00074A8D
Rythe's Studio Key FormID: 0001BC2C
Salmo's Key FormID: 00029189
Salomon Geonette's House Key FormID: 0001DA8B
Sancre Tor Key FormID: 0000A23F
Sanctuary Well Key FormID: 0000B258
Satha Dalvilu's Key FormID: 000982A7
Scinia Crypt Key FormID: 000568AD
Sea Tub Clarabella Key FormID: 000738DF
Second Hunter's Run Key FormID: 0018D13F
Secret Cell Key FormID: 000838CE
Seed-Neeus' Key FormID: 00029211
Seridur's House Key FormID: 0001DA8E
Serpent's Wake Captain's Key FormID: 0007B73E
Serpent's Wake Key FormID: 0000A26E
Severius Atius' Key FormID: 00022BAF
Sewer Gate Key FormID: 000274F5
Shameer's Key FormID: 0002918A
Shardrock Key FormID: 0018BA0E
Shiny Ogre Cage Key FormID: 0001EC48
Shrine of Dagon Key FormID: 0001F14C
Sigil Keep Key FormID: 00093EF5
Sigil Key FormID: 0009504C
Sigil Key FormID: 0009C225
Sinderion's Key FormID: 00068B05
Skingrad Castle Key FormID: 0002C461
Skingrad Castle Silver Key FormID: 0002C460
Skingrad Chapel Key FormID: 00069B17
Skingrad Dungeon Key FormID: 00035F8D
Skingrad Guardhouse Key FormID: 0002ADAC
S'krivva's Key FormID: 0000A07C
Slash 'N Smash Key FormID: 0001D200
Sleeping Mare Key FormID: 0000525D
Small Key FormID: 000366BC
Smoke Tomb Inner Key FormID: 00083FB5
Smoke Tomb Outer Key FormID: 00083FB4
Smuggler's Key FormID: 000A943C
Soris Arenim's Key FormID: 0002C677
South Watch Tower Key FormID: 00053FF2
Southern Books Key FormID: 00026085
S'rathad's House Key FormID: 00022BC5
Stantus Varrid's House Key FormID: 0001D359
Stonewall Shields Key FormID: 0001D156
Storage Room Key FormID: 0000C1FC
Storeroom Key FormID: 00025099
Summitmist Manor Key FormID: 000837D1
Sunken Sewers Key FormID: 0009588D
Surilie's House Key FormID: 0002918B
Surius Afranius' House Key FormID: 0001DA98
Talasma's Key FormID: 0009853D
Tamika's Key FormID: 0002918C
Tarnished Ogre Cage Key FormID: 0001EC41
Teekeeus' Key FormID: 00025067
Teinaava's Key FormID: 000693DA
Telaendril's Key FormID: 0006FDA8
Tertius Favonius' House Key FormID: 000177F1
Thamriel's House Key FormID: 00022BC0
The Best Defense Key FormID: 0001D204
The Bloodwork's Sewer Key FormID: 000677DB
The Copious Coinpurse Key FormID: 0001D154
The Fair Deal Key FormID: 0000A075
The First Key of Dark Hate FormID: 00014D63
The Gilded Carafe Key FormID: 0001D202
The Main Ingredient Key FormID: 0001D153
The March Rider Key FormID: 000034E9
The Second Key of Dark Hate FormID: 00014D64
Three Brothers Trade Goods Key FormID: 0001D206
Toadstool Grog Key FormID: 000974E8
Top Deck Key FormID: 0000C1FD
Toutius Sextius' Key FormID: 0002918D
Trentius Mausoleum Key FormID: 000CA22C
Trenus Duronius' House Key FormID: 0001D35A
Tun-Zeeus' Key FormID: 0003597C
Ulrich Leland's Key FormID: 0003F31A
Ulrika Ulfgar's Key FormID: 000982AA
Umbacano Manor Key FormID: 0002B455
Umbacano's Key FormID: 0002B456
Undena Orethi's Key FormID: 0002918E
Underpall Gate Key FormID: 0004E151
Ungolim's Key FormID: 0000A07B
Urasek Lockup Key FormID: 000CA6DF
Usheeja's House Key FormID: 00022BC4
Uuras' Key FormID: 0002918F
Vahtacen Ruins Key FormID: 0005401E
Valen Dreth's Cell Key FormID: 000950C0
Valtieri's Key FormID: 000693D8
Valus Odiil's Key FormID: 0002921F
Varel Morvayn's Key FormID: 0000A260
Varon Vamori's Key FormID: 0000A079
Vilena Donton's Key FormID: 00029217
Vilverin Chamber Key FormID: 0006C323
Vilverin Sepulcher Key FormID: 000C76CD
Warden Kastav's Key FormID: 00035DAB
Warehouse Key FormID: 0001D203
Wariel's Key FormID: 00026836
Waterfront Sewers Key FormID: 00026089
Weebam-Na's Key FormID: 00035986
Well Key FormID: 000084D3
Wellspring Cave Key FormID: 0006B396
West Weald Inn Key FormID: 000979ED
White Stallion Lodge Key FormID: 000908C1
Whitmond Farm Key FormID: 0000CBEC
Willow Bank Key FormID: 000034ED
Wumeek's Key FormID: 0001EB7E
Try really hard to NOT give yourself a key just because you are stuck and too lazy to search around. You can seriously screw up the games quest flags and potentially break the game. Also, with the latest patches you should never have to worry about the game losing an essential item. YOU might lose an important item, which makes me wish there was some built in system for retrieving lost goodies.
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