I know it's not ambi... but
http://airsoftbuddy.com/index_eprodu...roducts_id=267 is the original part...
http://airsoftbuddy.com/index_eprodu...roducts_id=558 is a TSC ambi selector.. but outta stock.. usually if you email them they can order it in but takes a few weeks. Also their shipping can be outragous. Also just realized that Qlong wrote about the same part from Ehobby above