James,
If you want to speak to Brits working as Flight Instructors in the U.S, give Anglo American in San Diego a call on 001 619 448 9149, nearly all the instructors there are Brits, speak to Chris the owner or Mark Chief Flying Instructor (both Brits), they will be able to answer your question about instructing in the U.S.
Regards,
GPS Approach.
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Aargh, that was the taxiway we landed on!