WOW, what a great looking gun! While I am not sure exactly where it might have been made, I can offer the following:
We know what dozens, if not hundreds, of New England fowlers look like.... and
We know what dozens, if not hundreds, of HVF New York fowlers look like.... and
We know what dozens, if not hundreds, of Penn. fowlers look like....but
What do Southern (Virginia/North Carolina) mid 18th century fowlers look like?
This gun looks to me like what a modern maker would come up with if you asked him to build his interpretation of a mid 18th century southern fowler.
Also, it looks like it might be associated with the KIP fowler in RCA vol. 1 No. 16
I have heard of others (2) that also might be associated with your gun and the KIP gun.
What an interesting gun!
Al