BGlass,
I don't believe there is a common (i.e. inexpensive) die that will do what you need, however a gunsmith, homeshop machinist friend, or machine shop should be able to make a simple "push in- drive out" die that will last long enough to make enough cases without hardening. It only needs to have a straight taper hole with the small diameter part smaller than the case neck. Then the cases will chamber for fireforming.
Mike