So I finally got to thinking about what you said here.

Where did you find the valve? What kind of establishment would stock those? Any ideas?

 

I got it from a local industrail supplier called Gregg's. Its a Canadian company, mostly western Canada. They sell supplies to auotmotive and HD diesel repair shops. I don't think that they have them in the US.

Could try some of the local custom truck outfitters. Like the ones that put the service bodies onto trucks.