Hasty suppressor: two-liter soft drink bottle, fastened to the muzzle with a hose clamp. If the barrel is too small to fit the bottle tightly, build it up with electricians tape. No ATF approval needed, throw it away when no longer needed.
I’ve heard of the 2 L. soda bottle suppressor but I thought that worked only for one shot.
Slingshots launching M-80 cherry bombs sound like fun, tho. Especially at night; do the rioters plan to disperse when the sun goes down?