Complete reservation boundaries from the BIA's TAAMS program and BLM's cadastral survey shape files for American Indian reservations. It seems BIA is not contributing datasets for reservation boundaries which is not trust data and BLM is not publishing the cadastral survey boundaries for reservations. These are needed for federal use and not provided.
My guess is that the census tiger products are going to have what you're looking for.
"The legal entities included in these shapefiles are:
- American Indian off-reservation trust lands
- American Indian reservations (both federally and state-recognized)
- American Indian tribal subdivisions (within legal American Indian areas)
Main tiger site: