This is the same vendor that I bought mine from. Great price & free shipping. Just in case anyone is in the market:
http://cgi.ebay.com/ebaymotors/Athena-Big-Bore-Cylinder-Kit-Yamaha-WR-250-R-X-08-10-_W0QQcmdZViewItemQQhashZitem2a110e6c54QQitemZ180674784340QQptZMotorcyclesQ5fPartsQ5fAccessories