l like 00247's suggestion to repair that part.
Mosler went out of business in 2000, and even then that handle was already an 80 year old part, not exactly something they had right on the shelf to sell someone
There is no place these days to just call and buy a replacement handle like that.
If you do not have a local safe technician or welder or handy man, you could probably send the handle assembly to this person to repair it for you or machine some replacement parts to match:
http://precisionlockandsafe.net/MachiningSafeRepair.htmlYou could also go to the Facebook Safe & Vault Collectors group, upload those photos to show them and ask if any of them have a spare handle to sell you. The members there have squirreled away boxes of safe parts over the years, so they're a good resource if someone is looking for a unique part.
https://m.facebook.com/SafeAndVaultCollectors/Or you can try my personal favorite, hang out on ebay for a few months looking for a spare handle. Sometimes they pop up for sale, but you may end up in a bidding war and pay hundreds of dollars for a rare safe part.
I found a similar looking handle that no one purchased, but it is not quite like the one you are looking for:
https://www.ebay.com/itm/384792284581/Good luck,
Squelchtone