You should be able to use a section of drill rod for a new firing pin retaining pin.
These pins are often very tight and after many years are frozen even tighter.
To remove, use a "starter pin punch". This is just a standard punch cut off to a 1/2" working length. The shorter length prevents the punch from bending and flexing, dissipating the force.
You can also often use a nail set.
If possible, use a smaller size dead blow hammer.
Get the receiver well braced on a no move-no bounce setup on a wood block with a hole to pass the pin.
Set it up on a FIRM surface. A concrete floor works well.
If when you strike the pin the receiver moves or bounces the force is dissipated and the pin may deform, locking even tighter in place.
If needed, have a buddy help brace it in place.
"Usually" pins are driven out from the LEFT side. However, some don't.
Look at the ends of the pin for any signs the pin has locking splines on it.
Often pins have short lengthwise grooves or splines on the end of the pin to enlarge the end of the pin and hold it in place.
The pin has to be driven out from the NON-splined end.
