Apparently they sale the membership cards to tourists as souvenirs
I had a card making me an astronaut from my Major Matt Mason toy. Does NASA have to give me a job?
No, they don't sell membership cards, many of the tribes are just not very discriminating about who claims membership because the tribes need to swell their numbers to keep their status as a sovreign nation. I know the local tribe accepts anyone who claims any amount of Indian blood, no matter where they are from, even Mexico.