Not sure about the current production. They are (were) mainly used in X-ray machines and image intensifier setups.
Do note there are many of these 100 mm lenses with different specifications, and also very different optical capabilities used on a modern camera.
The specification to look for is 100 mm f/1.6 Rodenstock Heligon. There are various models of these as well, but I think all should behave quite similar.
Keep away from the f/1.5 model as it is much less useful due to its design.
A final point, that applies to all Heligons, is that they are very heavy because of the large high-refractive glass elements inside.