There is currently an auction claiming to be a vintage prototype, but it looks more like an International variation. Follow this link to check out the
Star Wars Luke Skywalker Grey 1978 X wing Prototype Sample NO ELECT,4 guns!!!! auction and decide for yourself if it is a prototype or actually the European bilogo version of the Battle-Damaged X-Wing, which was moulded in grey, with black engines, and lacked the electronic components found on the North American version.