Back during my high school days, most of us kids, started out with single shot shotguns. One thing they all had in common, was what happened to the firing pin when dry fired. You would literally hear the end of the pin roll out the barrel. Now, if yours is like ours use to be, you had a retaining screw on top that fit into a flat, on the main body of the firing pin. Then you stepped down at a radius where you have the actual pin.
OKAY
Back then you would just go to your local GS and he had a drawer full of these and charged you about three bucks for one. I suspect most smiths still have a bunch on hand so just take whats left of yours and give them a try. Forget about a model number as it may not work on these old shotguns.
OPTION;
Our wild bunch was not into trendy stuff and tried to save all our buck for shells that we could hunt with on Saturday. We didn't even like paying the three buck for pins so I started making then out of screw-driver shanks. Mostly drill press and file work. We got pretty good at it as well. My dad didn't even miss his screw-driver. ....
Good luck and;
Be Safe !!!