Pain and Piety was quickly gone everywhere when it first was released and there has been rumors and talk about another print run, or that perhaps was already in the works. Who knows how, but in the UK Pain and Piety is back and stock and it appears other retailers are marking the box set as a GW direct only.
So if you missed it...... Better get on it. Anywhere else in the world though as of the time of writing... hold on and see if it comes around.