Positive votes for the other solutions! The method I used is also another easy location to get the cheev! Also if your playing a 2 gamertag local co-op you have to do this in a single playthrough to get this cheev.
-Play Episode III, Chapter 4 - Defense of Kashyyyk in Free Play (also possible in Story).
-Pass the beach area when you lower the tall wooden door. Enter the area with the downed ARC fighter in the mud.
-DO NOT KILL THE TWO BATTLE DROID COMMANDERS ON THE LEDGES. They will keep calling in for and endless supply of Battle Droid Reinforcements. I'm pretty sure there's is around 10 or more Battle Droids that try to surround you.
-Destroy 300 droids. Cheevo unlocked!
(Credits to risseless' Fire in the hole! solution! Positive votes!)