Oklahoma has 3 main requirements:
1. You are a member of a recognized tribe
2. You work on the tribal land associated with your tribe (it doesn't sound like you exclusively work in tribal land, I'm thinking you may not meet this requirement)
3. You live on land associated as belonging to the tribe.
Oklahoma asks for significant documentation on this as well. Please click on the following link: https://www.ok.gov/tax/documents/511Pkt-16.pdf and review the information on page 15, column1, under Tribal Income