A few deades ago, if I needed a new heater core, a radiator shop would fabricate one exactly like the OEM using my original nozzles.

Might be able to do that nowadays if you can find a capable radiator shop run by an old timer.

Caveat: BE SURE to pressure test before you go to the trouble to re-install it! I had a few apparently pass the pressure test at the shop, then fail another test a few days later.