The first overbore with a Suzuki piston is .5 over. this is what you want.
This leaves 3 more bores. You won't need a new sleeve anytime soon.
The 2003 kfx80 is a green Suzuki LT80.
http://www.powersportswarehouse.com/p/Kawasaki?aribrand=KUS#/Kawasaki/KSF80-A1_KFX80_(2003)/CRANKSHAFT/KSF80-A1-2003/I11I1118E1321
At the bottom of the parts list is the piston sets (piston and rings). $46.99