Literally for weeks I've been "farming" the factory in Pier 13. While I've gotten lots of drops during events and the money per energy is good, I've literally never gotten a single one of the armor pieces the factory supposedly puts out.
I've had the same issue with the helicopter in the army base. I was farming the tea house in china town and did get one of the vehicles once, but outside of that it seems that the drops simply aren't happening. I haven't completed a map since the South End Projects and Junkyard - so is there some rule that if you aren't close enough/haven't completed enough previous maps that the drops don't exist?