All you need to do is go to a nav beacon or USS and chase the guys chasing the Pirates. If in doubt, scan the ship being shot - if it has a bounty/wanted, then the guy chasing it is a BH.
Edit: stick to USSs. I've tried missions at nav beacons and the kills don't always register. Easy way to find them: go to anarchy system, SC towards the star, nav beacon or station, and when close slow down all the way to lowest possible SC speed. The USSs will "come to you" and when they do they'll all be within drop out range, making them very fast to get into.