When repairing military avionics, you have to use the exact parts approved by the military from sources supplied by the military. The government works very hard

When repairing military avionics, you have to use the exact parts approved by the military from sources supplied by the military. The government works very hard to make sure that parts for its aircraft are available, even if they are expensive. If the parts aren't available then you simply can't repair the unit without some sort of arduous waiver process. Anything else is a breach of contract at best.