Thanks very much; this was really helpful!You might consider using something like Am-Steel line to replace the center board pennant: http://www.defender.com/category.jsp?path=-1|10391|311417|314170&id=749705
If you want to go with 'wire rope' then any West Marine store will have the right diameter stuff and the fittings that you might need. WM would also likely have Am-Steel or equivalent high tech expensive line.
There is a WM in Haverstraw on 9W if you are in West Point, NY and they sell all of this stuff by the linear foot.
Good luck.
Was it steel? If so, I'm pretty sure just purchasing a spool from West Marine or another supplier would do the trick.