I am with Dave b. on O1 steel, it is easy to work and heat treat in the home shop, I always keep some on hand and get it from McMaster-Carr or MSC.
I just got a copy of "Gunsmiths of Bedford, Fulton, Huntington, & Somerset Counties". I hope you have or can get your hands on a copy. There are lots of lock plates shown that are not rat tail style. Three that I thought worth looking at (if starting with a Siler plate) were a John Amos on page 50, a D. Defibaugh on page 70 and a Jacob Meier on page 113. The variations of hammers is also interesting.