U.S. Copyright regulations are found in title 37 of the Code of Federal Regulations (C.F.R.). The library has a print set of the official C.F.R. (Mulberry Wing, ask at Circulation for specific location) Electronic versions are available through the Government Printing Office (GovInfo), Lexis and Westlaw.
HeinOnline offers full historic coverage of the C.F.R., which can be useful when faced with an issue based on previous copyright regulations.