If you have police scanner audio, then you should definitely include archival NASA radio recordings as another option.
Nice work, BTW.
(liveatc.net seems to be the most well-known website for live atc audio)
It sounds like they just don't want you to create an app for livestreaming contents of liveatc.net and that they allegedly own all rights to the content.
Maybe you could contact them, and ask if you could use some recordings.