It's a bit hard to tell from the photos -- but it doesn't look like much more than the dial and combination lock body are missing. From what I can see, there don't seem to be any relockers (and thus no relocker plate to worry about), and the mounting screws are still even there. It doesn't look like you need much more than a new lock... and it looks like whatever was there previously was pretty close to a standard template. (If so, then just about any modern combination safe lock could go back on there and work?)
If your locksmith couldn't help with that, though, then I'm sensing that I'm missing something. (Which I'm sure one of our folks here who's far more experienced with servicing vaults will quickly point out...)
You may also want to try the folks at antique-locks.com: there are a bunch of regular posters there with intimate knowledge of some of those older vaults.