One of my battens broke over the summer and I replaced it with a fiberglass one from West Marine. It cost about $10. You'll need the exact measurements of the missing batten. On my DS II, the top and bottom battens are the same, and the middle two battens are the same.
Their web site is <A HREF='http://www.westmarine.com'>www.westmarine.com</A>.
I need to pick up two battens also and have found them also at Annapolis Performance Sailing. I think they're slightly less expensive than West Marine. Pell