Need Top End Rebuild Kit For 2004 Polaris Preditor 50Please Help

[Preddy 50]

I just picked up a preddy 50 for my 6 year old and it starts fine and idles great but bogs down when throttled. It has 56 psi compression therefore i think I need to rebuild the top end but I cannot find a rebuild kit. Does anyone know where I can purchase one or if there is something else wrong with it. PLEASE HELP!!

Thanks