Having been nearly everywhere and done almost everything other than Deep Caverns, I thought it strange that I had never had the opportunity to work for the Free Drones or the Protectorate.
According to the wiki, if you agree to leave the Protectorate supply train bandits alone and lie to Captain Herve so that he drops the investigation, a Mysterious Lady is supposed to approach you at a Lower Underrail metro station at some point (I gather it's in Core City near the large BRIAN graffito). I met the requirements (got the bandits to tell me they were Free Drones; agreed to leave them alone; lied to Captain Herve, and failed the quest to find the train) quite a while ago, but have never seen the Mysterious Lady.
Here's a current save file:
https://drive.google.com/file/d/0B79A4QtWqedISkxrOE9xSzc3UnM/view?usp=sharing