I am not prepared to state a specific mission in which you can do this, as there are many that contain hundreds of planes, along with hundreds of pilots.
However, here are some general tips:
The pilot is the hardest of the 'critical hit' locations to line up with. If you are directly behind the plane, you will not be able to see him due to the fuel tank directly behind the pilot's head.
You stand the best chance of scoring a critical hit on a fighter pilot by attacking the fighter from the side, and following it round.
The easiest aircraft to get a pilot kill on are the bombers. Slow, lumbering, and with an unfaltering course whilst in formation, these targets are your best chance of scoring pilot hits. Tackle them head on, or go in from the side. Again, attacking from the rear will most likely not work.
Hope this helps those of you in need of assistance!