There was a Duron 1.33?
I thought there was a Morgan core at 13x100 (1300) and an Applebred core at 10.5x133 (1400). I'll assume it's a Morgan, since the Applebred would most likely be coupled with DDR.
regardless, you are looking for a Socket A board with SDRAM and onboard video and audio?
You certainly aren't going to be finding anything new. Scouring eBay is probably your best bet. Be warned, onboard audio of that vintage may not be very good at all.
Pretty much anything you find that has the features you want should support that CPU. Note that you don't even need 133MHz FSB speed to run that CPU, though it would be better to run it at 10x133 than 13x100.
I'd say look for something with the VIA KM133A chipset or the KLE133 chipset. I think the KM133A may not have built in LAN, but the KLE133 does. I think the KLE is available in DDR and SDRAM versions, I think there were even some boards that supported either (but not both). I'm reaching back a littel in my memory, so some stuff is hazy, but hopefully accurate enough to get you on the right track at least.