The web site "Government Attic" has posted a PDF of some of the NTIA Government Master File (GMF). This file contains license and associated frequency information for federal agency radio frequencies.
This file appears to have been obtained via a Freedom of Information request. I have known several people who were able to obtain this same information by filing a federal FOI request.
Remember that this is the unclassified section of the GMF and contains no real information on federal law enforcement agencies or their radio systems. Even with that said, there are many interesting tidbits of federal frequency usage by other agencies.
https://www.governmentattic.org/41docs/NTIAgovtMasterFile_2021.pdf
