SOUNds like u just nee to repair what u have. rjatv is a good place to start. google him and bore ur cylinder if need be. mic it ( micrometer) order correct piston,bearings,and seals
John att www.rjatv.com has great prices and you can go with ground shipping because he has really fast shipping.
normally i can get parts in 2 or 3 days ground.
but that aside i have a .40 over cylinder that needs a good honing,(you'd have to hone it anyway to get the rings to seat.) and head. but you'd need a piston kit and gaskets