I have got onto the second island for a long time now but still havent found a helicopter... Until... I foundly got one that has cannons and is at your appartment. Its called Little Willie. Go to the save point you first get as soon as you reach the 2nd island. Its white and quite big. Go inside and up the stairs. You should see a door. Go through the door and stand on the heli-pad. It should ask you if you want to pay £3000 for the Little Willie. Buy it and Fly It!