I don't think Huber can subpoena documents directly from that facility, but he can file a FOIA (Freedom Of Information Act) request. I've listened to people not involved in government doing so, with mixed results. Sometimes heavily redacted, and sometimes it can take years for them to comply. I doubt if Huber would have the problem, but look at the games the FBI has played with the House, in getting documents related to the whole Russia dossier, and heavily redacting documents produced. Devin Nunes doesn't stop there, though!