If you are looking for this:
It is indeed out of print, and has been for almost a decade.
If you are looking for the 20th anniversary reprint with all the same stuff plus extra content, AKA this:
It exists in plentiful quantities, at online retailers and (at least American) comic book shops. You can buy it from the Telltale Store, and also from Amazon US
whoops you already got it. oh well my answer will sit here for all time showing that i'm dumb and dont fully read threads.