Object Rocket3 is a homing air target missile that you could use.
Depending on how you set it up
it could be used for Plane vs Plane via setting Fire to Rocket and Control to BasicPlane
or it could be used for Ground vs Plane via setting Fire to Rocket and Control to Basic
also possible to do a 'flak' gun with more standard weapons - something with an elevation offset, a linear shell, wide prox, low damage.
if only i could remember the settings for that sorta thing :]