Howdy this achievement is easy to get if you don't mind a tiny grind!
Simply load up the chapter The Outskirts on any difficulty (I chose Normal) and make your way to the final check point in the chapter. You will know it is the final checkpoint because you will be in a room with a breakable door and outside the door is a Taxi with one of the Medium sized "Buff" zombies standing atop it.
Simply lob a grenade
at the taxi and make your way right. On normal and easy you can pretty much avoid the zombies and run atop theexploding barrels. If you want to clear out the zombies every time to help towards Moonshine Massacre then that's cool with me. But if you're like me and just want to get it done as fast as possible... RUN.
Blow up the first barrel setting off a chain reaction of the others til the ones in the back of the truck blow. Once they do hop over the truck bed and lob another grenade
at the police car.
Now simply die by zombie attack and repeat a total of 5 times for the 10 cars in all!
TL;DR Watch this and Mafiapocalypse done here: