Go to Vercetti Mansion.. get the helicopter on the rooftop..
then go to the VCPD HQ Police Station( straight to the right side bridge heading north ) 
till you found the VCPD HQ Police Station..
Go to the locker room of the VCPD HQ and you'll find the cop uniform ( you'll have it after 
the mission Cop Land..) Once you have it you can enter any police stations and also army 
territories without getting wanted levels..

Ride the helicopter and go to Army Territory in the Escobar International near the airport.. 
land there.. go to the last place in the Army Territory..
and you'll find the Army Helicopter ( HUNTER ).. :)