If you can craft the common one make sure you have the follow Perks added to the Tech Ability "crafting" tree -
Efficient Upgrade - it has a 10% chance of upgrading your crafted item - This is what allows a common Armadillo to be upgraded at random during crafting. However it's advisable to also get - True Craftsman (Craft Rare) & Grease Monkey (craft Epic) as well to get a Rare/Epic upgrade whilst crafting. So if you craft a common Armadillo say 30-40 times you'll get a range of Epic, Rare, Uncommon and Common Armadillos.
I also run Ex Nihilo (20% chance of a free crafting) and bunch of other Stuff, my crafting Tech tree is virtually all filled in. It does kind of break the game a little TBF being able to craft upgraded items for "free" as you can then disassemble the upgraded items so one common Armadillo costs say 6 common and 4 uncommon but it could get you 1 epic which can be disassembled for 4 common, 6 uncommon, 4 rare, 6 rare upgrades, 3 epic, 1 epic upgrades - so you can see if you crafted 200 common, you'll get a whole heap of stuff extra during disassembly - like I said, it's a bit game breaking so I rarely use it like that and prefer to play the game as meant, using Gun/Clothes stores, disassembling captured enemy weapons/clothes etc.