An internet search should point you to Gen. Sumner's papers in the Wilson Library, U. of NC, Chapel Hill.
Quite a few of the papers have been digitized and you can read them on the web. The correspondence can tell you where he was in June, 1781, but not necessarily where his recruits were from. Still, there could be great clues.
You might find more in the papers by personally visiting the library and going through the collection.