"Washington appealed for any quantity that could be produced and state governments began encouraging domestic powder manufacturing which was virtually nonexistent at the time. The entire struggle would rest upon the efforts of Attwater, Munson and others like them to supply the army's needs until more plentiful foreign supplies could be obtained. In all, domestic gunpowder manufacturers produced only 100,000 pounds of powder from 1775 through 1777, but it allowed the struggle to continue. Things improved dramatically as France clandestinely supplied the Americans beginning in late 1776, sending over 1,000,000 pounds helping ensure the continuation of the struggle and allowing for the much needed victory at Saratoga in the fall of 1777."
36
May have even been more than that:
https://allthingsliberty.com/2013/09/the-gunpowder-shortage/
But 90% is probably about right:
http://www.universityarchives.com/Find-an-Item/Results-List/Item-Detail.aspx?ItemID=54674
"Washington appealed for any quantity that could be produced and state governments began encouraging domestic powder manufacturing which was virtually nonexistent at the time. The entire struggle would rest upon the efforts of Attwater, Munson and others like them to supply the army's needs until more plentiful foreign supplies could be obtained. In all, domestic gunpowder manufacturers produced only 100,000 pounds of powder from 1775 through 1777, but it allowed the struggle to continue. Things improved dramatically as France clandestinely supplied the Americans beginning in late 1776, sending over 1,000,000 pounds helping ensure the continuation of the struggle and allowing for the much needed victory at Saratoga in the fall of 1777."