I run batches of strikers out of 3/8 heavy duty garage door spring with excellent results. Face quench only shine that puppy up nice and smooth on the striking face. You are slicing off small bits of steel with your flint each time you strike and the smooth face works far better that a rough one. I strike the steel against the flint in a motion that I just can't describe but could teach you in about a minute and a half. About any stone that would have been knapped into a tool (flint, jasper, quartzite and a bunch of others ) will strike sparks. The stone has to be harder than the steel and well sharpened.
Finnr