Nankang quit making the 21-8-8 for a while, but they are available again.
I always rode 250's or 450's, so 04PSD's reccomendation of 22's may be more accurate for a raptor. I'd stick with either a 21-12-8-8 or a 22-11-8-7's standard buff hauler on whatever thickness wheels you prefer. Staying with an 8x8" wheel on a 21 or 22 inch tire, you will have a hard time bending even the .125 blue labels. The cheapest is probably to just order them from rockymountainatv.com with the above mentioned online coupons.