Are they present in the faction wars like in the video? I've only come across one and that was at the hospital.
I think the "destroy the helicopter"-mission in the hospital is the only time you'll find a heli in cs... Never got to take one down in soc... Lord knows I've tried!!!
Uh theres a helicopter right ontop of the roof of the freak museum in duty base.
If you mean a working helicopter there is a few in the NPP. I also saw videos of helicopters in the swamp but I've never encountered one.
You get attacked by a helicopter in the swamps on the leaked beta. You can't even blow the damn thing up, just set it on fire.