Have you tried Aircraft Spruce?
Trade-A-Plane?
A local avionics shop might be able to point you in the right direction.
Is Pioneer the same as Bendix (a possible model name or division)?
If do, search Pioneer.
Airpath also made B16s.
If the parts are interchangeable, they might be able to help you. If they aren't interchangeable, still call them, again they might send you somewhere.
https://www.airpathcompass.com/Here is an old thread about the compass....
http://warbirdinformationexchange.org/p ... =3&t=30803As the thread above indicates, there were thousands made by various firms.
With so many wartime examples out there, it's possible no one makes parts, as it might be easier/cheaper to just get a new one.
Also, if you know what parts you need, you might be able to buy one off eBay for parts.