We have a winner! Thanks everyone for all your suggestions. Mutual Screw and Supply, suggested by dedhed is exactly the kind of site I've been hunting for.

Google search is great, but sometimes it really screws with me (no pun intended). The secret to finding Mutual Screw is to search for "metric pin in socket stainless"... comes up as second link. As soon as you add "hex" or "torx" to the search Google sends you off on a wild goose chase.