For the record, if you wanted to make one, it would be pretty easy -- just use a chip socket adapter for the 6507 (if you want an actual chip from a console), permanently adhere it in the sockets, then drill a hole on the side, insert chain, attach keyring on other side......voila! Pretty simple.
The ones I (and, to be honest, countless others, the idea is certainly not a new one) made were game PCB keychains. I Dremeled all the rough edges off (so as not to snag a pocket) to smooth and then basically drilled a hole in the PCB itself to accomodate a simple keyring. They're pretty quick and easy to do, provided you have a press drill and a vice (both of which I do not have, so I used the old 'stand on the thing you're trying to drill and hope it doesn't hit you in the eye' method).