There is a lot of unlockable armor in Halo 4. Most of the Halo 4 armor sets don’t include armor for your Legs, so you have to unlock them separately.
Here is the list I have compiled of all the leg armor I’ve seen in all of the dev videos. I think I’ve listed all of them, but let me know in the comments if you find any missing.
Unlockable Leg Armor
All of these can be unlocked naturally in the game.
Contoured – Reach rank SR-40
Contoured CHVR – Unlocked with the commendation Payback – Master
LG-50 Bulk – Reach rank SR-23
Mark VI – Complete the Campaign on Legendary difficulty (solo or co-op)
Outer-plated – Reach rank SR-31
Over-locking – Reach rank SR-49
Recruit TIGR – Unlocked with the commendation Exterminator – Master
RG-63 Counter – Reach rank SR-10
XG-89 Narrow – Reach rank SR-35
Exclusive Leg Armor
Here is the list of leg armor that is only available from pre-orders, collectors editions, or console bundles.
Fotus – Included with Halo 4 console bundle
LG-50 Bulk PULS – Pre-order bonus from the Microsoft Store
Outer-plated CRCT – Pre-order bonus from Walmart
Over-locking WEB – Pre-order bonus from Amazon
RG-63 Counter FRST – Pre-order bonus from Gamestop
RG-63 Counter PRME – Included in the Collectors Edition of Halo 4
XG-89 Narrow RPTR – Pre-order bonus from Best Buy