The same place I find my extremely rare 440 Six Pack engines, HEMI engines and Dodge & Plymouth muscle cars.
The bad thing is that I don't ever give out my sources.
The good news is that I have a good line on a third Air Ram manifold.
I am not trying to be greedy with these it is just that I own two Tiibbys. One of the Air Rams I have now is technically for a Beta-II. That one will be sold when I get a third one (Beta-I). I would do a direct trade, however the trading party will send me theirs first, as I have lots of references that will back me up, and I dont trust anyone.