Are left handed Fender Custom Shop guitars always available?

Yes, but the availability of models is not constant. Batches of certain models are made for a certain period of time before fresh modes take over. We always keep left handed Custom Shop guitars in stock at guitarguitar.

Did Fender ever make left handed Nocasters in the fifties?

No, this is a concession made by Fender's Custom Shop to offer something cool and awesome to southpaw players. Lefties deserve to have the pick of the best, just as right handed players do, so we salute the Custom Shop for making these incredible Nocaster models available to left handed guitarists.