I've completed 9 campaign missions, and was loving the Buzzer ultra-light helicopter that I found after the 7th mission. I saved and quit for the night, and now that I've come back to continue playing, I don't see any Buzzer vehicles anywhere on the map. What happened to them? Do they only exist during certain times during the gameplay?
There are always Buzzers around. For example you can find them where the supply drop missions for the golden path are or near bell towers. I'd suggest, in case you already reside at your family's home (after doing the first mission for Yogi), buying a Buzzer (the sherpa outside your home sells you upgrades to your home, like a helipad).