That would be me. Unfortunately, the need to survive and complete projects I've undertaken for others keeps interrupting my schedule. The good news is that I'm in the process of finishing my last promised editing job, and told all my authors that it was now my turn.
To give the OP a short answer to his question — virtually none of the locks used on American rifles were made here. I haven't gone into the pre-1790s era very much but, of necessity, I've acquired some information along the way. Of course, about 99% of the surviving long rifles are post-Revolutionary and of those a huge percentage had locks made in three or four black country towns surrounding Birmingham, England. None of these were made by a single person. The gun lock trade was extremely specialized and the vast majority of the workers were small entrepreneurs, many of whom couldn't read or write and none of whom left any written records known to have survived. In fact, the only written records pertinent to a Birmingham export merchant that have survived include some firearms references but they are of no value for purposes of identification.
That said, some conclusions can be drawn from items that are dateable by other means and I expect to have some hard figures as to how many locks were imported. The numbers are staggering. This isn't to say no locks were ever made here, but so far nearly every one I can feel reasonably certain of can be attributed to someone known to have come from Birmingham or its environs. There are good purely technical reasons for this — like the fact that, in order to make a good lock, you needed steel. There was simply no commercial production of steel in America until much later, clearly illustrated by the need of the Springfield Armory to import it from England and Germany until after the Civil War.
