What's a compact or intergovernmental agreement?
A compact can be thought of as a "negotiated agreement between two political entities that resolves questions of overlapping jurisdictional responsibilities. (Witmer, Corntassel. Forced Federalism: Contemporary Challenges to Indigenous Nationhood. Volume 3 of American Indian Law and Policy Series. University of Oklahoma Press, 2006 (110-111)). When researching tribal law, common examples of compacts or agreements are intergovernmental compacts between tribes and states, or tribes and other tribes. Subjects of such compacts can include economics e.g. gaming; public safety, child welfare, education, taxation, law enforcement, and environment.
In New Mexico, tribes involved in gaming must enter into an economic agreement with the state, which then requires a gaming compact; or two pueblos might enter into a cross-deputization agreement; so, for example, a tribal officer from Pueblo A in pursuit of an individual who committed a traffic violation while traversing across Pueblo A can pursue and arrest the offender on Pueblo B if the offender flees onto Pueblo B's land.
When researching intergovernmental tribal compacts or agreements, here are some places to start:
NCAI --- "Tribal Governance" --- "Resolutions"
NILL --- Tribal Law Gateway --- "How to Find: Tribal Compacts"
Tribal Court Clearinghouse --- Tribal Law --- Tribal / State Relations
Tribal Court Clearinghouse --- Tribal Law --- Tribal Law Enforcement
Look to individual state websites for a state department or agency dealing with Indian tribes, for compacts between various tribes and that state. Example: New Mexico has a department of Indian Affairs. Searching the internet for the [name of the state] AND either "Tribal" or indian" may yield results. If you aren't finding anything, consult your friendly local law library reference desk for assistance.