If you join the Catalina 30 group on Facebook, there is a fellow on it who salvages C 30 parts regularly. The steering mechanism is a big project to change out. If you can't find a used one, the it may be cheaper to find a boat that already has wheel steering installed. It is a PITA to install as the C 30 had the steering mechanisms installed before the deck went on. Getting the steering quadrant, cables connected to the pedestal chain drive is a bugger. Good luck.
ps. Here's an interesting picture of the stern cut out on a C 30 exposing the rudder stock design: