Didn't know that also Defence bots drop nanites, so that's at least one incentive for doing the IFN mission chain on them Thanks for sharing.
I suspect any UG mob can drop them, but could be wrong. I do know that which nanite you get is based on maturity, with adjusted dropping from lower maturities, mod from higher, and imp from the middle. I've gotten the highest quantity from Badgers and Wombanas, but those are also my highest turnover mobs in UG.
You're right, I've looted nanites from all the other UG mobs myself. But never from IFN bots (and now I know I simply haven't been hunting them enough, or at the right time)
Don't think its been confirmed that dromia drop them. I can't seem to hunt many without falling asleep to test it.