After nearly 2 months playing reguarly with a low MR player (for whom Stalker flat out refused to stalk), I finally got the 3rd scan I needed so I'm done! Phew. That was an unnecessarily annoying grind.
Since it seems that your shadow stalker, Zanuka, Gustrag and the syndicate death squads all take a potential spawn for Stalker (eg it seems a mission can only have one of those attack) - it might be quicker if you make sure you clear any other marks, so only the newbie player has their stalker mark... so you're not getting all the other annoying people instead.