I think I found it:
Pennsylvania Gazette:
Perkin and Coutty at the corner of second and Spruce Streets, Philadelphia, beg leave to acquaint their friends, and Public in general that they carry on the Gun and Pistol making in all it’s branches, where gentlemen may be supplied with Guns and pistols of the neatest and best quality, on the shortest notice and most reasonable terms. They also blue and brown gun barrels In the neatest manner”¦.. May 2, 1781
Alas, it doesn't specify what kind of blueing they were doing, so it is no help at all. So that is a bust...
I did find a reference in Bivin's book to a bunch of guys armed with rifles and swords threatening a surveyer in early 1760s NC, which has nothing to do with the subject at hand but goes into my mental list of "Early rifle references from the South" and into the "Swords in the backcountry/frontier" list, though.