There's a nerd trader that sells them. Surrounded by turrets, can't miss him. Seems fairly rare. Not really sure what's the difference between the different colors of turrets besides a general "more expensive is better".

You can also find them in mansions and toy stores as a random chance

Green turret is like an uzi, red turret is like a minigun.

Red turret also has a little more health, I think, not that it matters much.

toy stores seem a little odd but thanks for the reply

Fun for the whole family

Can they be picked back up?