I am sure there are some gunsmiths that have a supply of hammers, if You don`t find them in the US I could make some research here in old Germany.
I have just seen some hammers offered at an auction:

http://www.egun.de/market/item.php?id=1729722

Send me a PM if You can`t find what You need for Your drilling. Is it a 9,3x72R ?

Kalunga