Easiest way to get this is with the buzzer. You can grab one early on just outside Khilna Bazaar - the first outpost you liberate.
Grab the M79. It’s a grenade launcher that counts as a sidearm, so you can fire it from the buzzard.
Fly around, following the roads, and take pop shots at any vehicles you pass. They normally have two enemies in each and two grenades will completely blow the vehicle and anything else within range. Chances of being shot dead are slimmer too.