I've only seen them in photos. The hardware store will have drawer locks that can be installed on the gas door successfully, I've done it on a number of Berlinas. These locks are often used on multi-door mailboxes.
No, but someone told me that they are standard locks for cabinets. I found one that looked like the drawing in the parts book and bought on eBay. It was one from a gas pump door lock from that period. $12! Thanks for the note.