I can't help you with a source of loaded ammo, as I think most of it is in the hands of collectors. I can, however, make some suggestions for forming brass that has worked very well for me. Of course, you can form from .357 Mag using an expensive form set or using a .30 Mauser die as an intermediate step, but I had significant brass loss and case life wasn't very good. You might want to try one of the following methods.
1. Get some .22 Jet brass from Graf's, if they still have some, and just use a tapered expander in your .256 Mag sizer to open it up. It will fireform upon the first firing. The case will be about .030-.050" short, but it works fine. So far, case life has been fine.
2. Exchange your extractor for one for a .223 Rem and go get some .221 Fireball brass. Size it in your .256 die and trim to length (you'll have to trim off quite a bit). This is a VERY strong case and seems to last forever. Naturally, it headspaces on the shoulder, but you should set your dies so the .256 case does that anyhow for decent case life.
Plan one is my lifetime plan for my Merrill pistol, as it has to use a rimmed case. Plan 2 is my lifetime plan for my Contenders to keep them shooting.
Hope this helps you. Let us know your experiences.
RonF
