I think you should try FAA - there are plenty of FAA medical examiners in the UK. The FAA website will help you find one and the CAA listing of examiners will tell you which other countries they can examine for and to what level.
You should be able to operate your heli on an FAA PPL while keeping it on the G-register as far as I know, although from memory (and it has been a while) you might not be allowed to take it out of the country?
Either way, as Moosp says, re-register it and keep flying!
Good luck!