You're not going to be able to just order the hammers, I wouldn't expect.

If it was me, I wouldn't refinish the wood. The old/weathered look is probably the route I would go, this is likely a job that's beyond the newbie. It would end up looking old and refinished instead of just old, if that makes sense.

Enjoy the shotgun for its heritage and don't let detractors get you down!

-Leverhead