For years Supercats have used something like fishing rod blanks. They are nicely tapered, can be had in carbon or regular glass, and come in thousands of different dimensions and stiffnesses. Bill Roberts once told me, "The advantages of these battens are that for the required stiffness they are the lightest weight and due to a special taper, they naturally bend in a desirable airfoil shape in concert with the shape built into the sail."

The problem is coming up with exactly what you want/need the first time since you cannot adjust them. They also break into sharp daggers if you fall into your mainsail.

Don't ask me how I know...