You really going to go with the "if the subpoena isn't on the internet then it must not exist" theory?
Who got it into your head that the cover letter for the subpoena was proof the subpoena wasn't an actual subpoena?
No I am going to go with it is a public document and if it exists you should have no problem producing it theory.
Where are all the Congressional subpoenas located? If you know of a repository for all of them let me know please. Not going to go file a FOIA.