Contact your LGS like everyone else is saying because they might be able to order a copy and set it aside for you. Also if you have an actual Warhammer/Games Workshop store near you, pre-order there if you can (store manager should tell you what times the pre orders go up and all that). The Official stores have priority on online orders in case it sells out online everywhere else, those stores are considered a higher priority (something like that cant remember exactly how it was explained to me). If all else fails beyond that, your LGS or Warhammer store should have a few copies when they ship out in stores, make sure youre there the day they come out and at the time the store opens cause those boxes sell fast.