I don't know if they sell the seater/crimper individually, but the "cowboy" series of dies from RCBS are all roll crimp. Also, for less money you could call CH4D and they have roll crimp dies. Or, rummage through the boxes of dusty dies at the gun show- which I've done numerous times.
If you have a set or can pick up a set cheap of .38 Special Lyman 310 dies, they should be roll crimp. Just get an adapter for 7/8x14 press. Problem is, finding them cheap anymore is the problem.
If I have an extra regular roll crimper laying around that isn't in a set, I'll throw it your way.