Low carbon steel for everything except for the springs and the frizzen. 1095-1075 or 5160 for springs and the frizzen. Case harden the low carbon parts once you have finished and polished the completed lock.
If you are going to hand forge a lock than I would recommend wrought iron. But you will need to learn how to forge the cock so that the grain in the iron flows with the shape of the cock or it may break in the neck area.
There are a lot of different metals that can be used you just have to find which ones you like to work.
The original locks for the most part where Wrought Iron.