I can't help you much with a new pump, but I have had "The Flying Dutchman" rebuild several water pumps for me that I couldn't find a new replacement for or that the lead time was very long. I worked on a mystery diesel in an early 70's Worthington air compressor that turned out to be a 2.2 liter GM 4 cylinder diesel (4 stroke), never heard of one before or after and still can't find out what the engine really is. It needed an injection pump (had a CAV pump leaking thru the weep hole but ran well) and the water pump was starting to seep. Re-sealed the pump and sent the water pump in and it's been working great ever sense.
If you at least have a partially intact core water pump maybe it's rebuildable.