Paulson shows 64 chips here, but I know there are some new colors out there (maybe because of the lead issue):

http://gpigaming.com/pdf/US_Chips.pdf

Spragg once told me that there are alwasy new colors being introduced and/or discontinued, so the real number of colors is unknown.

I take it individual colors are not for sale? At $200, these would be about $3.50 per chip.