All of this considered, as a practical matter an attorney should get a release from the client and obtain certified admissible paper records of all such witnesses in the ongoing fight. Agencies can be very courteous in getting you these documents as they know it helps them stay out of Court and live testimony. Sometimes there are even strategic reasons that the records are better than a live witness. If a Court rules that a witness is unavailable for a state subpoena, the evidence can come in as government records, business records, and other possible hearsay exceptions.
However, Touhy and its progeny cut against the fundamental right of criminal defendants to compel the attendance of all witnesses necessary for their defense. We as criminal practitioners should continue to litigate and attack the Touhy doctrine and get courts to narrowly define it according to its original holding.