The best way to get this and waste no command points is load up level 24 in act 3.
Go to the left and head north and you will find a rocket and a grenade. Grab both and head back to where you started and three soldiers will appear from the left and i believe will only appear if you grab the grenade aswell. Kill all 3 with the rocket. You could then use the grenade to kill yourself or you can head along the road to the right and you will come to 3 enemies and another rocket which you can grab and use on those guys, you can only get two, the red guy and one green as the other is to far away. If you survive that continue south a little and you will see another rocket, grab that and to more soldiers will come from the east. Then let the trucks kill you and rinse and repeat. So thats 7 guys in about 1 minute and this will also next around 2500 command points, not much but better than wasting 15000 on 3 rockets, Then let the trucks kill you and rinse and repeat. Assuming you have at least one rocket kill this will take no more than 7 runs of this.
You could also use this for the grenades here but killing yourself with the rocket after the first 3. Although there are better missions for this.
I recommend having your troops fully upgraded with delta force training so they are tougher, faster and have a better item drop % as the first 3 enemies you kill have a better chance of dropping an extra rocket to use on the guys along the road and then use the other rocket there on the truck and soldier next to it.