I have two of these and would love to know also!
I do restore these at times. If locked, just drill out the lock and replace it with new 3/4" cam locks....keyed alike. A lot of times, these were not locked and the top can be lifted up and off? Nothing too difficult about getting into them? Paul
www.severngaspumps.com
If the lock has stamped numbers on it, your local lock smith shop can probably cut you a key to fit. I did this for an old Coke machine.
Do what Paul said. That is just a simple cam lock. Drill it out. They are $6 at Home Depot and you can get two that are keyed exactly the same by looking at the key number on the package. They are the EXACT same lock. It will not look different.
Or if you get the door open or pick the lock, it’s just a large nut on the backside to remove the lock. Then go to Home Depot and get the same cam locks for $6.
-Steve