Navaid went out of business in April of 08.
You have several options. 1) buy a trio autopilot head. They are compatible with the navaid servo and will sell just the head. 2) find someone who bought a trio head and wants to sell their working navaid head. 3) fix you navaid head. Motor failure appears to be a common problem and the motor can be replaced by a capable person. I hate to send anyone over to the dark side, but the best place for info on this is on the forums section of vansairforce.com . Do a search for navaid and you will get a lot of info on this.