I mean initially someone had to sell them all the guns so they could fight the revolutionary war. Was it Britain who sold them and they then they revolted with those very guns?
The Dutch republic was one source of weapons and ammunition. They were sold to the Americans via the small island of St Eustacius (in the Carribean). This arms trade was one of the reasons for the fourth Anglo-Dutch war, which the Dutch, badly, lost.
See .e.g. Barbara Tuchman's First Salute.