Tim,  First, welcome from one Tim to another.  Next, I would look for new dies being readily available from sources such as Midway, Natchez, etc.  As to brass, you should be able to form brass from new or once fired .45-70.  May lose a few to wrinkles, but I often get my brass for low cost or free so it works well for me.  I do have the ability to take it down in steps with a .38-56 die, but can’t say I see much improvement in my reject rate.  If you reform, be sure your starting brass is truly round and uniform on the mouth.  I use the size die in my RCBS set to form the brass, by the way.  No need for special form die.

Tim Tomlinson