HMV are offering the Locus Helmet and Spartan IV Avatar Suit with pre-orders of Halo 4.
It's interesting that the leaflet suggests it's the Helmet that comes with the pre-order and not just the skin. This promotion isn't mentioned anywhere on HMV's website so might just be an in-store deal.
Big thanks to Dust and Echoes for the tip!
- Cowboy Out.