Copyright law in the United States is primarily federal law. Thus, copyright cases are mostly decided in the U.S. District Courts, the U.S. Courts of Appeals, and U.S. Supreme Court.
For call numbers, dates of coverage, and locations of court reporters, see the Gallagher guide on Court Reporters.
U.S. Supreme Court (Print)
Use annotated codes (check the case annotations accompanying statutes in Title 17)
Use West's Federal Practice Digest 4th and its predecessors (look under the "Copyrights and Intellectual Property" topic)
Look for cases cited in footnotes in relevant treatise sections and law review articles
Look in the index to American Law Reports--Federal (ALR Fed) to find relevant articles