These are deep dark mysteries, for sure. Different authors have researched the numbers of gunsmiths in the colonies at different periods and have come up with low numbers for the first third of the 18th century and very low numbers for the 17th century. Grinsdale's "Flintlock Fowlers" indicates that fowlers were the first guns made in America. He re-stated the numbers of gunsmiths that Kaufmann and Sellers documented in colonial America (east coast). 17th century- 5 or 8 gunsmiths, total. 1700-1725, 4 or 7 gun smiths total were documented by those 2 sources. 1725-1750, 12 gunsmiths documented by each of those 2 sources. In contrast, by 1775 the numbers jumped to over 100 documented gunsmiths working in the colonies. These are likely underestimates but the trend may reflect the population boom from 1750 on, bringing the need for more tradesmen to meet demands, and the colonial system, where good were supposed to be purchased from the mother country, was also weakening somewhat after 1750.
We assume that most of the work of the early gunsmiths was repair work and re-stocking. The purchase of rifled barrels suggests making new guns from new parts, doesn't it, since shot out rifle barrels can be readily "re-freshed". Without any further data, I'd speculate that early Virginia rifle guns pre-dating the influx of Germanic tradesmen looked like the earliest English rifles, with less refinement.