I’ve seen the old stuff, but unless you have a shop near you that deals in used, you are going to be hard pressed to find it. Even then it’s hit and miss.
You could easily make your own with new or used track and a pair of pliers. On the outside of the curve, pinch the bottom edges of the tie together, and on the inside of the curve bend the bottoms out. Thats basicly what the manufacturers did originally.
I understood exactly what you meant, and I think you are right about who used to make it. But I still think it would be easiest to make your own by bending the ties of normal track with a pair of pliers.
All American Flyer O gauge and Hafner trains do use track like this. Don’t forget about Eruopean manufacturers, though. All the trains made by companies like Bing, Marklin, Bub, etc. used this kind of track. Hornby of England is an exception, though, but pretty much all the German companies made this kind of track. In fact, AF and Hafner were certainly copying European practice in making their track. It can be hard to come by. Good luck in finding some.
Until this thread I wasn’t aware of modern manufacturers attempts at banked curve O gauge tubular track. Ives produced it’s own version way back in the early 1900’s. I have enough of this type track for a complete circle (roughly 27" dia.) including one curve that has provisions for electrical connections ( permanent type lockon). The third rail is, as the surfers say, totally tubular…a simple hollow tube held in place with what’s best described as C clips. These in turn are mounted to the ties like a rivet using metal and insulated washers. The ties themselves aren’t stepped like in the above picture although the angle created is about identical. I know this isn’t an answer to your search for wide radius, banked track. I just found the topic worth commenting on.