Arctic char available in North-America
My first reaction was to be surprised by your question as Arctic Char is fairly common in Alaska, I didn't realize that it is hard to find in the lower 48.



It's closely related to salmon, so salmon would be a reasonable substitute for most applications.

This article tells more of its range in the wild (far north) Arctic Char. It is farmed in the US Farmed Arctic Char but not in huge numbers. I'm not aware of it being known by any other name.