Ask on the gunbroker.com forums lots of gunsmiths post there including
me and somone would surely know. Theres probably quite a few choices
for what you could use as for hardness I don't know off hand I could
probably find out but it would take time, which I currently don't have.
Sorry.

P.S. have you thought about just buying a new bolt? Would probably be
cheeper time wise in the longrun.