Episode 9 Crisis at Coney Island starts off with 2 Red Foot Soldiers with Plunger Guns.
They tend to stand and fire from the edge of the screen.
Stand in the middle of the screen and Hit
as the plunger nears you.
Their shots are slow and easily timed
You can farm all 10 just on those 2 guys.
If you do not get it with them, there are at least a dozen more thru out the level