I looked and looked and I couldn't find it. I guess I already gave it away! (Though I don't remember -- it could have happened).
I have gobs of Slot 1 style Pentium 2 and 3 CPUs, and a couple of P3 "flip-chip" style CPUs, but no AMDs that I'm not using (of course, I have two Athlon XP-M Bartons that I'm using happily at 2.6GHz that I'm in no mood to part with).
I'd strongly second Benn's suggestion... Just do it EBay.
Just make sure your motherboard supports the Athlon XP style Socket A chips before you buy one of those. Some boards do and some don't (they had different power requirements and stuff even though it was the same physical socket). Actually, I just checked it. The only CPUs yours doesn't support is the Athlon XP with the 200MHz (400MHz in marketing-speak) FSB (which was only the 3000+ and 3200+ Bartons originally, but others were later added).
I'd look for an Athlon XP 2500 or 2600 CPU with the 333 MHz FSB.
Something like this would be a perfect fit:
http://cgi.ebay.com/AMD-Athlon-XP-2600-1-917-Barton-Socket-A-CPU-333-FSB_W0QQitemZ130163339704QQihZ003QQcategoryZ44935QQssPageNameZWDVWQQrdZ1QQcmdZViewItem