You can get a 54mm piston for it.
It's the piston for the 105cc kit. You don't need the sleeve. Just bore the one you have. The 105 sleeve is only .015 thicker than the stock sleeve and I can't see .0075 a side making a difference. Mind you that the cyl wall are going to be thin and that reliability may be a issue.
It's a 125cc piston out of a honda bike I think.
2000 GNC 5N\
2001 GNC 9N \ 40+ class
2004 GNC 9N /
2014 rock crusher "GO tortoise GO!"
2016 Byrd Rooster
Father of the "11" time National champion,and worlds fastest woman ATV racer
A few fast LT80's
250R~300cc's
300ex
350 Rancher
Kymco Mongoose
Survivor of the 12 Hours of ATV America 04 and 05