Where Can I Find a Large Concave Mirror for Heating Water?

[supersteve921]

Im trying to figure out the best way to heat a about a bottles worth of water, my idea was to get a concave mirror and focus it onto some small radiator like a heater core. The thing is I can't find a large concave mirror, so I was thinking about using a satalite dish but I can't think of a way to make it shiny enough, you guys go any ideas?

 

[Andy Resnick]

Edmund scientific sells giant Fresnel lenses just for this purpose.