what are you trying to do, exactly?
I think you may be bargaining for more than you want. If you use a valve, you have to mount it and change them when they go out.
If you're just trying to make an easy way to kill the engine, take your ignitor and put a piece of rubber on the top and pop it over the end of the exhaust pipe.
I'm not trying to "shoot down" your idea. By all means, be original. However just consider what it is that you're trying to do.
BTW: I don't think you can purchase just the shut off valves that you're talking about. If you're talking about the ones I'm thinking about, they regulate air, no liquids. You may try home depot or something.
IMO. I would make a custom air filter and hose, and put the shut off there instead. Bottom line, if you cut air or fuel, the engine will stop.
Good luck and let us know!