There is the Disciplineglobalmobile.com website, which sells all things King Crimson, you could literally purchase their whole catalog there, they also have downloads so you don't have to wait.
I've been a fan since the 80s, so every time something new comes out, I just purchase the CD because I like having the whole package with the artwork - it's a holdover from my childhood when I'd read through liner notes while listening. I still do that.
Ebay also has a number of sellers selling used CD's too. I've completed collections by looking there.