Richardson s Rec. Ranch, Ltd., Gateway Rt. Box 440, Madras, OR 97741 Sells stone. Sells tools, stone, reproductions. My favorite steel striker is the edge of a common file.
All files work, but the best ones have smooth edges.
You can grind the edge ribs off with a grinder if you want. Just pick up rocks everywhere you go and strike the steel against a sharp edge and watch for sparks. You will be surprised at what all will work. The edge of the rock has to be sharp to shear off little bits of metal from the file. The sparks are globs of burning metal.