I understand that they are very rare, and I would suspect very expensive. Cannot imagine that one would be better in any way than a clean Summar.
I had a Summar that John at Focal Point cleaned the haze and fungus out of, and even w/ the etched lines from the old fungus it never flared (with a hood), and was one of the best, if not THE best Leica 50 lenses that I ever owned, and that is comparing it to the 50 DRs, the collapsible Summicrons, etc.
Why not try one of the collapsible 50 3.5 FSU lenses? They're a different optical formula than the Elmars, but image in a very similar way and are a heck of a lot cheaper. You won't have to keep a fingernail untrimmed in order to set the aperture either. The Industar 22 lenses I owned were very sharp.