Armour (the correct - British - spelling)

Advice please on getting my last piece of armour (apart from the Haunted helmet).
It’s chest armour and it says available only through halo waypoint - so can anyone steer me in the right direction?

UA/Base Security [W]: Reach Waypoint Career Milestone 30 and unlock the Yes, Sensei achievement from Halo: Reach.

That being said, Waypoint exclusives, Preorder Bonuses, and the Haunted Helmet do not count toward Armory %, so you appear to still be missing something else.

Thank you for your reply.