There were three main producers of the standard claw mounts that seem to match the ones shown. They are Bock, Ernst Apel Wuerzburg (EAW), and Eric Recknagel (ERA). All of them would have provided the parts "in the white" and the front rings "hooks" pressed into the hook plate (which would be dovetailed into the "sattle"). The rear ring is adjustable for windage ("mit support") and would have been bought long enough to adjust for elevation and mill the feet. The rear hooks would have been milled and fit to the base by filing on the bottom side of the "slider" (this takes the slack [Luft] out of the fit up. The bases would been fit to the barrel, soft soldered, contoured, engraved, and blued. Once all this work is done, by any qualified gunsmith, it is pretty difficult to know who produced the mounts (or whether the "production" was done by the maker of the parts or the unknown gunsmith that installed/fit them up).
Mike