There are 3.
Attu Warrior, in Heber City, UT <--which I've worked on and flown in.

Hot Stuff, in Indianapolis, Indiana

And I forget the third one, but I know the owner of Attu Warrior, and he told me there are 3. I'll see him again this weekend, maybe I'll ask again.
P.S. Just looked on Wikipedia which says there are 5, so that's wrong.