You are gonna get a TON of people that tell you that you can ONLY get the LOCUS Helmet through a King of the Hill App (which no longer works after 31st). This is not true. It also comes on a DLC card. I know that for a fact because i have 2 in my possession. Suffice to say that ANY DLC that comes with a preorder is RARE as it becomes dated. The LOCUS isn't any rarer than Raptor armor or Deadeye, in fact the Locus Helmet was easier to obtain than both and was FREE if you used the app.
Pic of the DLC i have (not my pic but same card) http://i.ebayimg.com/t/Halo-4-Dlc-card-3-add-ons-Raptor-skin-Locus-Helmet-Spartan-Emblem-/00/s/NjUwWDQyMw==/$T2eC16RHJGIE9nnWqySlBQyVGiBkFg~~60_35.JPG