There was an original set of chips of 20 chips issued in 1994 (corresponding to the silver anniversary of the WSOP). Then 2 in 1995 (that is the Hamilton chip plus another), then 4 more (1997, 1998 and 2 in 1999). Then they changed styles to the Bud Jones chip for the final three (2001,2002,2003).

There are plenty of them out there, don't pay too much.