AFAIK, there is no bolt-on big-bore 'kit'.
i know there is a cam, and with enough money, i'm pretty sure the cylinder can be overbored, re-coated, new piston installed, have a stroker crank made, have whole motor lightened-balanced/blueprinted.
might as well buy a multi cyinder/more powerful bike too.
also, there is a 660 motor, but i'm pretty sure it's still 625cc.
however, and you've likely already been told, your money would be better spent on having the suspension sprung and revalved for your weight/riding style, a new pair of tires, and multiple trackdays/schools of learning.
a wise sage once told me: 'if you're riding that bike to 100% of it's potential, you should probably quit your day job' LOL, and i was transitioning from an EX500 to a CBRF2 at the time wayy back in 1996......