I just got this game (Beat it in 2 days lawl) but Where do you get rpg in campaign or quick play?

Its found in the Intervention mission, when you have to take down the helicoptor.

ya it kinda took me a while to figure it out but this is how u get it: when u reach the part of the boat where the helicopter is which to our pistol and run behind the fork left and u should see a hand symbol on the top screen, tap the icon on the bottom screen and run after the fork left untill it hits the machine gun and u should see another hand symbol tap it and ull have an rpg and 3 rounds

i thought that you didn't explain it properly so i thought id have a go at it. In the Intervention mission you will get up to a part where there is a fork-lift it is next to a crate on the right, walk up to the forklift and tap on the hand symbol above the weapon selection symbol and then it will drive into some enemies and then stop, take out the other enemies around you and then walk over to the forklift and then look down and you will see what looks like a bazooka but its an RPG (Rocket Propelled Grenade) launcher then if you want it tap on the hand symbol as instructed above. I hope my advice helps you in some way.