Where to look for air parts?

[davepl]

I'm looking for two parts that were sold as GMC accessories across the line but would be far more common in heavy duty trucks. Mine's only a 2500/3500 so it's outside my area of knowledge!

In any event, I'm looking for the air horn "Solenoid Control Valve" and the little air tank reservoir pictured below. I realize I could get any of these off eBay in modern form, but I'm hoping to find period-correct stuff.

I assume the tank is small, like well under a gallon.

I'm more asking for "where to look" than "does anyone have these", as I doubt they're very common, but don't know where to search.

Thanks!
Dave