I got Nakura 5.5g rollers from ebay for under £10 delivered i think from ebay but i also bought some basic no brand ones in the past from my local kymco dealer before for about £6-£8 i think.
Taipai Scooter Assassins do both im sure but delivery is usually a few weeks from the far east. If you get the rollers and try them and it feels too light you can fit 3x alternate 5.5g and 3x 6.5g (stock ones that are in now) to get the same result as using a set of 6g ones, just make sure you keep them spaced properly ie, 1x 5.5g then 1x6.5g etc so its balanced out. I know another member tried the 5.5gs in his and he said his reved to high for his liking, mine is a 2008 but his was newer like yours. He did the above to run it at 6g and prefered that, so if you buy 5.5g ones you have both options of 5.5g, 6g, and 6.5g if you mix and match what you have.