The Native American democracy that the U.S. founders were most likely to know about was the Iroquois Confederacy.

~ https://theconversation.com/before-the-american-revolution-n...

and from other native groups you'll see many statements like:

~ https://collegefund.org/blog/democracy/democracy-is-rooted-i...

IIRC there's a lot of material about the North-North-American fur trade origins piggybacking onto existing Great Lakes and other regions trade networks with the French and the British picking up political and trade habits from those peoples.

( Not a scholar in the field, just a broad reader )