KDXRIDER.NET

A NEW one will run you around $600 US. I have seen used ones on ebay for much less, but plan on having to send them out for replating in most cases (another couple hundred bucks). I know millenium if you send them the cylinder and your new piston they will match them. Don't know if the other platers do that.

I like the Wossner as they can take some punishment. I'v drilled holes in them, enlarged the lubricating holes on the exhaust side opened up between the skirts, taken material away to decrease the space to the gudgeon pin and chamfered the skirt in a few places. Apart from that they make them just how I like them for a forged piston. Actually the don't the rear port is the wrong shape in my opinion.

You could take a punt on a B being the right size. The ideas is the size it's made for the first time is increased by one for the next piston so A to B as it's worn just a bit. Having said the original barrels come in different sizes and you can see that stamped on the top of the barrel left side at the front. One of mine was stamped C so the next piston was D.
They do this so they can get a good fit as machining barrels from the factory can varie and still have the right tolerance.