Oh God, tell me you did not buy a 1.5 hp 4 stroke pocket bike. Love the frames and bodies but the engine is junk.
Get Slicks, go on eBay, search Tires for 49cc pocket bikes, and see what shows up. They have plenty of tires for sale.
Think you need 110/50 x 6.5", that's the rear, the front is 90/60 x 6.5" I believe.