A medic friend of mine likes acting and has all that cop gear and some training. He'd certainly be able to die convincingly, at least.
If you want to improvise cop uniforms (like for people in the background), I can get you the uniform shirts (and possibly a few belts) if you can find navy pants, black boots and white undershirts/t-shirts.
I might be able to get you an ambulance, but scheduling the time/ location might be a problem.
The disaster drill is for explorer scouts/cadets in the emergency services field, mostly from Washington. It's taking place at a boy scout camp north of Monroe, just up the road from the lake Roesiger park we stopped at for the fall colors tour. I'm not sure what the scenario will be since I wasn't involved in planning it this year, in the past we've had a riot and a plane crash. Here's last years website, the pictures might give you an idea of what I can find as far as equipment/people:
http://www.geocities.com/explorerjesd/index.html