You can buy it from comic shops (find your local shop here) or digitally.

The first three collections of DIE are now available.

They’re called DIE: FANTASY HEARTBREAKER, DIE SPLIT THE PARTY and DIE: THE GREAT GAME. If you’re looking for a local comic shop, this site can help. It’s also available from book stores, and online retailers.

DIE’s fourth arc, THE GREAT GAME, will begin in May. If you want to pick up the new issues as they come out, you can talk to your retailer to pre-order them. They will likely be collected in November.

You can also buy individual issues digitally, or subscribe. You  can do so here, which is a nifty thing to do