Rotor Blades

Try a hacksaw blade. Run a cord through the hole at each end, and bow it to the droop you want. Tie it off and tape the rotor blade to the saw blade. Put it in warm water, and let it sit. Take it out, let it cool and see if it is enough sag.

On the few fling wings I've built, I've been able to produce droop by heating the blade in hot running water, bending the blade by hand and then running cold water over it to cool. Takes a little practice but works for me. If you are very careful, you can put a bend a blade by hand until you get curvature you want but the chances of breakage really goes up.