This list is to show the unlocks go in each specialization.

Unlockable	How to unlock
1st Set of Armor	Reach specialization ranks 2-4 to unlock the entire 1st set.
2nd Set of Armor	Reach specialization ranks 7-9 to unlock the entire 2nd set.
Specialization Package Mod	Reach specialization rank 10.
Specialization Visor	Reach specialization rank 6.
Weapon with Alternate Skin	Reach specialization rank 5.