Hello James,
Yesterday I visited two flight schools (at two different airports) here in Houston. Both schools have had UK instructors recently, but unfortunately, both instructors have moved on. (One of them just left a month ago.) So, I'm afraid I don't have any contact details to pass along.
Don't give up, though. Perhaps (like GPS approach in the posting above - - great info!) other PPRuNers will know of some UK instructors at US schools, and can assist you. I will also keep my eyes and ears open, and let you know of anything I may find out in the future.
Good luck,
McD