Paintball Co2 Canister

[sapphire_moon]

I am trying to set up a "Death chamber" and am wanting to use a paintball Co2 canister because I have easy access to them. However I just don't see how I am going to be able to modify it without blowing myself up! Has anyone ever done this? If so can you tell me how?

I see the pin on top which is pressed down to let the Co2 out, but how could I get that to work?

If not what kind of places can you buy a Co2 tank at (I'm in the states)

Any help would be appreciated!