At tribe's website.
See NILL catalog record for all available versions of the constitution.
See NILL catalog records for other tribe materials.
United States Tribal Courts Directory. By A. Schwartz and M.J.B. Hunter.
Tiller's Guide to Indian Country: Economic Profiles of American Indian Reservations. Tiller Research, Inc. (see older version online at the Internet Archive)
Tribal Leaders Directory. (BIA)
How to Build a Tribal Legal History. Indian Nation Archives