I took a mission last night to kill 12 pirates in a neighboring system. I am curious....is the only way to find these pirates by interdicting them out of supercruise? I went to the NAV beacon and not a single one from the faction that I need to kill. I managed to kill 7 before I gave up for the night but it took almost 1.5 hours for them to appear. If that is the case I will not take anymore of those missions.....
you did the only sensible thing in the absence of RESes, you went to the nav beacon. SC prowling is even more hit and miss, but I have a tip for you, carry some valuable cargo and you won't have to scan for them, they'll come to you (in both the Nav beacon, and SC as well).
I hate carrying an interdictor (and obviously cargo), it's a waste of a slot, especially on combat missions. If it were up to me, Disco Scanner, Fuel Scoop, FSD interdictor, 2t of 'cockpit storage' (think of it like the trunk of your car, lol) and the warrant scanner would not take up a slot but be MUCH more expensive and increase in cost with ship size.