Bill, they are around but I don't see them often. There was one on Ebay about 6 months ago. Try asking Chris, Bassel, or Anthony (tag on AZ).
FYI, I thought about buying that one on Ebay but figured it was probably more trouble than it was worth since I can shim something pretty quick. Something to consider. 4 jaw indep. chucks are great for getting stuff dead center but can be a pain as well. If you are running an operation on multiple parts, you get it centered, mark 2 jaws and only move those two when putting parts in and out. The problem comes in when the diameters are different, the wider the range in diameters the greatly they will be off-center. Then if you doing multiple sized stuff like say drilling/boring a few ferrules, then cutting a tenon, then whatever.... you have to recenter those chuck jaws each time. The 4 jaw is a great tool just know it can be a pain as well.