Advanced Warfare Legendary and Retired Gear Unlockables will be earned after the Supremacy DLC comes out.
Advanced Warfare Legendary and Retired Gears will be unlocked after the next DLC Supremacy in which you will be able to earn both of those gear sets through supply drops and you will be able to collect all the different pieces to completing the sets. The Legendary set is a new one that will be introduced and we probably will see legendary weapons like we see in Destiny which are fun to unlocked or earned through Legendary Supply Drop Loot gameplay.
The Retired Gear set is a gear that you will be able to earn too but will be taken away from inventory and you will keep it if you currently have it. Here is the Legendary gear that you can unlock in advanced warfare after the Supremacy DLC releases.
Below find the Advanced Warfare retired gear set that can only be earned now but if you have it you can keep it.