Have you talked with the Cooper folks? I'd imagine they would be the source for dies. If not I'd ask Todd Kindler at the Woodchuck Den. In such a small case I'm sure you could bump the shoulders back with arbor press dies if that's what you wanted to use. BTW, what gun are you thinking about doing this to? What are you going to do about the RF vs. CF change, or are you thinking about a Contender?
BTW, from the outset I thought they should have made the HRM on the same dimensions as the CCM and sold rifles with interchangable bolt faces. Reload if you want to, if not buy rimfire ammo!