Google is your friend......
Simple methods for molding fiberglass and carbon fiber
Ok I hate hearing that to but really there is tons of information on line about making fiberglass molds. What you might not realize is that lost of fiberglass molds are actually made out of fiberglass. The process usually goes something like this apply quick release. I think painters tape might work.... put I think the pro's use wax. Then spray that with gel coat, then apply fiberglass. Let harden and pop it off. and there you go one mold.
Don't use spray foam unless you want a mess.... it's good for attaching to thinks then carving, but it would make a flimsy mold.