Hose clamps are not a quick release solution- it will take you are a would be thief the same amount of time with a screw driver to loosen the clamp, depending on the tool used.

You can find hose clamps in just about any store that has either a hardware/home improvement/DIY section or automotive parts.

Side note: if using the hose clamps on bare metal bars, it's best to use some sort of friction agent to both protect the metal and keep the light from rotating on you.