AFAIK, only some of the Sock-939 mobos with ULi chipsets had the ability to use AGP and/or PCI-x video cards. nVidia absorbed ULi and that feature died - Via made chipsets that supported Sock-939 w/ just AGP. Good luck. I know that at least Asrock and Gigabyte made ULi mobos. I went on ebay, drilled down to Socket-939 mobos and then searched on AGP and got 93 hits.
If you don't want to chance used, find one you like on eBay then use the price search engines on the model no. to perhaps find a new one.
.bh.