Guides & overviews are often the easiest introduction to the original legal documents. Consider starting with a secondary source and use its bibliography to locate original sources.
The collected reports and documents of the United States Senate and House of Representatives, including annual reports of the Secretary of the Interior. Available in print and selected years online.
The government-published US Code (abbreviated U.S.C.) and commercially published US Code Annotated (USCA) incorporate all current federal law into topical "titles". Title 25 is entitled "Indians" and covers much of the law governing federal relations with Native America. The Congressional Record contains the transcript of floor activity for the US House and Senate.
The Code of Federal Regulations (abbreviated CFR) incorporates all current federal regulations into topical "titles". Title 25 is entitled "Indians." The Federal Register is the official daily publication for rules, proposed rules, and notices of Federal agencies and organizations, as well as executive orders and other presidential documents.
We no longer receive current issues in paper.
United States Reports (U.S.) - or - United States Supreme Court reports (U.S.) -or- United States Supreme Court Reports, Lawyer's Ed., 2nd series (L Ed 2d).
US Reports contains decisions of US Supreme Court cases.
Consider starting with law review articles for introduction to specific cases. Both the WestlawNext and Lexis-Nexis Academic databases (see links below) include both law reviews *and* court decisions.