What U.K. teas are NOT available in the US?

Are there any U.K. tea brands that are not easily found in the US? I have family who like hot tea but I don’t want to bother schlepping stuff over if they can find it at the local grocery store. Any ideas? I know PG Tips and Twinnings are easy to get in the US, what about other brands?

Maybe whittards? (I probably spelled that wrong) My inlaws always go there when they visit.

Also, there's a bunch of fancy teas if you go to any of the palaces. It's overpriced, but also from a royal site so that has value to some people.

A lot of the stuff we saw at the palaces was put together by Harney.

I always found that anything from M&S went down well. 

Whittard and Harrods teas are all very nice!

Whittard is a safe bet. (So is their drinking chocolate!)