There are over sized pistons, but I don't know if there are any big-bore cylinder kits. I do know that there is a hotrods stroker kit from wiseco. That along with a 1 or 2mm larger piston might get you close to 400cc. There are suspension products available for most any ATV, including your Raptor.
Yours truly, sincerelly, love always, Josh aka The DirtDemon.