My Cody Helm Winchester broke a firing pin at about 300 shots. Had Keith Kilby install a new pin right out of a parts bin at the factory. New pin broke at about 200 shots. Drilled the broken pin in the lathe for a piece of music wire. Placed a set screw in the old pin body to hold it in place.  Has thousand s of rounds through it with no problems.  Several of my rifles have music wire firing pins. None have broken yet. Music wire needs no heat treatment at all. Very tough and flexible stuff. Your local hobby shop should have what you need. I also use it for false muzzle pins.

Actually if you can just replace the tip of the firing pin with a piece of Piano wire of the correct diameter. I highly doubt that it will ever need to be replaced again...

Or.. you can buy a new made one here: (You need to Login or Register to view media files and links)