I believe most of them don't need to be unlocked but do need to be crafted on an Expert Workbench/Forge.
http://wiki.cohtitan.com/wiki/Base_Defense_Items
That's weird. My Super Group has no access to the Elite tier of base defenses-- and it has all 3 tiers of work benches. My Villain Group can access them all (and has about 70 of them in the base so far... entirely for visual effect of course).
I am very confused right now.
I forgot how to unlock the Elite class of base defense items. I have them on my VG but am looking to get them for my SG now. Anyone remember how to unlock these?