And the form tool need only be the half or full size of the bead, not the full width of the roller, to reduce chatter and tool pressure. On this side of the Pond "gauge plate" is called flat ground tool steel. You'd want the type that can be oil or water hardened and tempered, if you were going to do that. It should come fully annealed, or you will have to anneal it first.
I've used automotive spring stock, too, annealed and hardened and tempered.