Some specific guards and sideplates appear on more than one early colonial rifle that is stocked in American wood. This, and that the engraving does not match other engraving on these guns, or on other guns believed to be made by the same maker, leads to a partial consensus that such castings were commercially available. That they were imported is also supposed, because of their similarity to some European examples.
I think by extension, it is a common belief that many/ most of the rococo guards which are for now "solo" examples were also imported. I don't know how one would research any of this. But I'd not be surprised if a clever young scholar or an iconic master had some clues.
