They first appear in the 40's or so. Reynolds made one of that basic type, cast in aluminum. They are really modeled on hand-made stems brazed up from steel tubing; GB made them from both Reynolds 531 and Accles&Pollock Kromo tubing; and then, in the 50's, GB made a cast aluminum (hiduminium, actually) version that was based on the steel ones. Most aluminum stems from the 50's through to the early 70's were more or less of this style; brand names I've seen on them include GB, Reynolds, Pivo, AVA, Philippe, Compe, Jun, and... oh, I don't know, there were a lot of them.
Lugged stems, in a style similar to what you showed, but made for threadless type forks, are made today; they're steel, handmade, and expensive.
interesting - and thanks for the details! I found a similar ttt that I am happy with at a swap meet today (guess there really were a lot of them, and not just the French...). I was specifically looking for one with the back end of the clamp sticking out slightly, and was provided
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I have seen the lugged stems you mentioned (Rivendell/Nitto ones?) though none seem to have the nut at the top or the extended top part in the back. Either way, my search is over - thanks for the help!