You can obtain Greedo from the Cantina after completing Episode 4 Chapter 3. Just go into any game, either Arcade or go into Free Play mode of any Chapter, and:
if you have 2 controls: Make your main control Han, and your second one Greedo. Turn off all cheats and turn on Adaptive Difficulty (I am not sure which ones actually affect the achievement, but I did not get it until I had my above listed settings). Then just use your Han controller and shoot at Greedo a few times until Greedo breaks into pieces. Your achievement will unlock.
if you have one control: go into any chapter and choose Free Play. "Pick Han and start the level. Then switch to the other player with Y. Press RB until you have selected Greedo. Then switch back to Han by pressing Y again. Then shoot Greedo until he breaks."
~Credit to JeOuweBaasAFCA for the one controller method.