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...FWIW, depending on how accurately you have dated your frame, there were plenty of reasonably OK frames put out by manufacturers over the years that were solid bikes, made with relatively good tubing, that did not have integral rear derailleur hangers on the rear dropout. They were not top of the line frames, but still pretty good ones. Stella comes immediately to mind, but there were others. If you go back far enough the percentage of OK frames without integral rear hangers on the dropout increases dramatically.

In fact, recently while searching for period appropriate derailleurs for a late 50's bike, I ran across very few of them that did not have a claw hanger attached in the Ebay pictures. The co-op suggestion is a good one, if you have one. OUrs here always had a small parts bin filled with them, all attached to the derailleurs they originally served.