Firstly, thank you everyone for answering my Q and apologies for not replying sooner, we've been away on holiday and I've been constructively ignoring the yank tank until I got back. The replacement part is somewhere in/over the Atlantic so I will have to tackle the issue soon.
If its that tricky I would crack open the old one and have a scout for an EEPROM part, you might be able to read this and find where the VIN is using a basic cheap EEPROM programmer (Amazon or similar)
This sounds like doing a thing, but honestly I didn't even understand some of the words you used so I feel this would be a project all its own. I will take it on if no other option presents itself, and you may expect a PM if I do!

Another option: If it's only the alternator output from the PCM that has died, find out if you can get a conventional regulator that fits that alternator or bodge one to fit it.
Unfortunately the PCM talks to a number of other modules so it has also thrown an EML. So to effect the bodge I would also have to wire the check engine light into the oil pressure light (or similar) which I feel goes beyond bodge and into rather dishonest territory!
Several companies around the country who specialise in repairing ECU,s .
BBA REMAN are probably the best known, so might be worth starting with them.
This is where I think I will go tbh. I feel like they should be able to either repair (potentially using components from the one that's coming) or reflash the US part.
In any event I will report back as the misadventure continues.