why would you need the oldest one? just look on ebay or any other online bidding site. Or go to your local computer store, like a refurb place...
I think the oldest card (from what i can remember) is a ATI Mach64 card year 1996 is when it came out i believe.
I have an old ATi Rage 128, those cards sucked. I bet he's doing the trade in thing where ATi gives you 50 $ credit for an old card. FYi, they accept any card.