I have some old TheMightyHobie18 battens. I will try 2 of those.

The company that makes those battens for Hobie, makes bigger ones and they are cheap compared to most battens. I will look for one that is about twice as stiff.

To answer the question about who makes stiffer battens, almost everyone that makes battens. They make battens for big boats that are wider and thicker. They are normally sold through sailmakers. The stiffest batten I know of are the carbon over aluminum honeycomb. They are sold under the black magic and other names. If you need something stiffer than that, you can order sheets of composite and cut then into strips with a table saw or laminate wood carbon.