journeymen,
Note that 9.3x72R rifles in good shape are often used with modern commercial ammo or equivalent "nitro for black" handloads, even if proofed for black powder. It is likely that you can have a new barrel made but given the cost and the fact that black powder proofed 9.3x72Rs are still often used with appropriate Nfb handloads, I wouldn't recommend it. My cousin has taken whitetail with his BP proofed rifle, which is more than likely very much like yours, if yours is also one of the ubiquitous small frame underlever, single locking lug tip up rifles. They are a lot of fun and very useful if used as originally intended.
Mike