Available in HeinOnline.
The set has no index of its own, but the National Indian Law Library posts a topical index to tribal court decisions in the Indian Law Reporter. You can browse by topic or search for keywords. And you can search the full text in HeinOnline.
A second set of the Indian Law Reporter is in the Classified Stacks (1974-92) and the Clinical Law Program (1993-).
Commercial Online Services
Federal and state cases are available in online services such as Bloomberg Law (general federal case database), Lexis Advance (general federal case database), and Westlaw (Federal Native American Law Cases).