It's a tough job but Mike Adams gives you a leg up with this tipsheet. Indian nations are independent and generally do not have FOI laws, but there are ways of getting around that. Adams lists websites and public records that might have information on dealings Indian nations have with entities that DO keep public records. For example, look into the municipal bond market, the National Indian Gaming Commission, and the SEC. He also gives examples of investigations he did into specific tribes and where he found success. He further profiles the National Indian Gaming Comission in a packet available for mail orders.