Shedim have the same access to information that all humans do. Graduating classes are public records, it's not hard to pick 5 magical colleges from the day they opened until now. That should provide many time more candidates then they would need. It doesn't take any kind of special magic insight to handle that.
Then it's simply doing some career research, some personality profiling, and then tracking them down. If you figure a force 10 spirit is as intelligent as most boosted mind a human can be, it should take on them any sort of time to work out exactly what they are looking for and to be a better judge of character then any mire humans could be.
Most are probably in the matrix under their original names. Find a couple that are desperate, and sure they may well know what they are dealing with and the dangers involved, and i'm sure a some number will react violently. But finding one that is desperate enough to deal, or find on that can be maneuvered into being desperate should be very doable, for something as powerful as even force 6-8 force spirit let along 9-12.
Spirit pact aren't very common, and they aren't easy to track down even for fairly powerful mages.
Or the other rout, freshly graduate mages, young egotistical arrogant 18-20 years olds. Certain of their invincibility, sure they have heard about Shadim, but they are way to smart and way to good to ever be tricked by something like that. Offer them power, immortality, hell just get'em layed a couple times, and I have no doubt some would be very happy to sign up.
Knowledge of threat doesn't guaranty understanding of a threat, experienced folks get in trouble all the time.
