If i remember right someone had bought a GZ cheap to fix and sell or ride and something was wrong with the engine. I look on ebay on occasion just to see whats there for the GZ and saw an engine listed and thought I'd pass the link along just in case since hens teeth are more common than some GZ parts it seems.

http://cgi.ebay.com/ebaymotors/2005-suzuki-gz-250-gz250-motor-engine-8-315-miles-_W0QQcmdZViewItemQQhashZitem19be322a94QQitemZ110565141140QQptZMotorcyclesQ5fPartsQ5fAccessories