I have a pair of Y tracks by K-Line, I think they are 21 inch radius. The Y is self re-setting or will allow you to use a switch motor with it as it has a small hole for a switch motor to mount to the throw bar. Email me at phillyreading@gmail if interested in the Y tracks.
The 21 inch curves are very close to 21 inches, 21.5 inch diameter circle as I just measured the tracks.
Lee Fritz