Very unusual- reminded me of some of the oddball locks we’ve had here in the UK like Wellington and Webster. They were unique designs and relatively small volume numbers, and were hard enough to obtain even when in production, but once stopped the supply dried up overnight. There was no lingering stock or leftovers around at all. Plus their unique design, shape and sizing proved a nightmare for anyone trying to retrofit anything else. They were a lot more recent than what you have there, so if yours was an oddball design and a rarity back in it’s day, it’s going to be a challenge tracking any now.
It’s great you want to keep things original but endless searching online and hunting around salvage specialists is probably all you can do. Good luck with it all and if you go down the custom manufacture route I’d recommend having a comfy chair and a bottle of your best tipple at the ready 🙁nod):
