Wasn't there a gunsmith operating in one of the NDN towns, prior to the french incursion into western PA? I'm thinking Venango in the late 1740's or early 1750's, but may be wrong about the location. 1747 seems to ring a bell.
If that smith was operating so far from the western edge of the frontier, at that early date, why wouldn't Henry travel to the Scioto Valley, provided there was adequate compensation?
From the trade companies perspective, it would be good business to have a gunsmith to repair NDN guns in or near a trading post. Or, it is possible that the NDN agency contracted with Bayton Whorton and Morgan to hire a gunsmith to repair and refurbish their arms in one of the larger villages, especially in light of George Crohgan's "adventure to the Illinois Country". While that is speculation, that is a possibility worthy of research.
NDN agencies did hire gunsmiths specifically to repair guns for the local NDNs. Creamer in Southern Illinois comes to mind, in the very early 19th century. I believe that Hawken did repair work for the NDN agency, located in St. Louis, so that appears to be a fairly common practice, though at a later date.
I believe that the Proclamation line was designed to prevent settlement in the NDN country west of the Appalachian Mountains. Trading posts were exempt, or at least not bothered.
Interesting stuff, worthy of speculation and further research.