250-500cc Big bore kits, where to go

I need some advice please.............I own and race a 2006 WR 250 with a FMF Gnarly pipe on.
It is time to replace the piston and rings again. I was looking at somehow putting a big bore 300cc kit on.
A few questions
where will I find the big bore kit, everybody seems to only keep the 4T stuff?
Will the FMF still fit or will I have to replace the pipe as well?
Will the standard 250 Mikuni carburetor be good enough (I will play with the jetting to get it right)

The problem in South Africa is that there is only one dealer / importer so the availability and prices leaves a lot to wonder about.

http://www.cafehusky.com/forums/showthread.php?t=4237

It's a start.

eric gorr does a 274 or 284 cc for the WR

Can you get your hands on one of the 300 kits from the "Special Parts" catalog?

Part #8000H0915

IMO, that would be the way to go. Your pipe and carb would still work.

Thank you gents
I appreciate your assistance.

I am sorry for my ignorance but where do I get to see the "Special Parts" catalog?

Thank you Coffee.