I'm surprised you can find a mid century PBX in a junk yard, and that if you could the parts wouldn't be completely destroyed by the elements. Is there some kind of indoor tech junkyard somewhere?
HSC is the equivalent for lower-level electronic parts. They’ll also be closing down in January.
https://www.nytimes.com/2009/02/05/technology/personaltech/0...
They've been around for a long time. Jobs and Woz apparently bought parts there for the original apple computers.