Do a web search for PepperBall products. These work in standard paintball guns, but should work in 12-gauge shells too. I'd try an inert or marking round first, just to make sure the gelatin capsule doesn't rupture during firing.
It's tough to get those products without police or agency I.D., but I'll bet *someone* here knows how to get around that.
33 posted on 05/02/2013 8:24:22 AM PDT by Charles Martel
(Endeavor to persevere...)