If it is old it is probably a wooden one. I would suggest to make a new and re-use the metal parts. It isn’t as difficult as it sounds, nor is it expensive. All you need is the official drawing from the associations secretary (or use the old wood as a template), a power jigsaw, a power drill and some sandpaper. I have just finished one (for the third time) for a fellow sailor and I made lots of photo’s of the process. I am working on an essay with these photo’s that will explain how to do it. I hope to publish it on WIT in a few weeks time.
BTW there is also an unofficial drawing available here: http://www.wayfarer-international.org/WIT/maint.repair.ref/CB.rudder/unofficial.rudderstock.drawing.pdf