I think I read somewhere that the CAA has not appointed people who can do revalidations outside the EU; although who knows why they are so hard to find.
It's not that the CAA appoint - it's a capitalist market - so if an examiner applies for the IRE, is qualified, can pass the course etc and can justify the cost of maintaining it outside an EU state then it happens. Problem is that the costs of maintaing such a qualification are high.
There is definitely one in Florida and possibly one in Arizona.