I dont know where to find the case you are asking for but I have painted a couple of cases.
Ideally the best way is to strip the paint off of all the metal parts, spray them with primer and then pain them the color you want. For some this is a pain in the butt but you do get the best results.
If you do not want to go through all of this I would recommend at the very least getting a sanding pad and roughing up the paint. After you rough up the paint wash the metal with soapy water and get all the dust off. Do not touch the metal with your hands, wear latex gloves. Dry the parts thouroughly and then blow them dry with air, be careful if you use the canned air it can leave residue.
Buy a good can of spray primer, spend a few bucks on the quality of the paint you use and you will get better results. Give the metal parts a couple light coats of primer as per the directions on the can. Let the primer dry thouroughly. Once all the parts have dried the required top coat time you can apply your color. Do not touch the parts with your hands betweent coats, your fingers will leave oils that will repel paint and make lots of little boo boos