I too am an SJ23 owner, sailing on Lake Norman in NC.
Here is the link to San Juan Tech Tips: SJ23 San Juan 23 sail boat Tech Tips
The site is maintained by Bob Schimmel, who sails in the waters around Vancouver. Gene Adams is the guy who bought the molds and the parts inventor and still sells spares for the SJ23.
The site is continually updated and is a wealth of knowledge about the boats. The pin you are seeking is pretty generic and can be found through Schafer Marine. One major thing to check is the centerboard and the mechanism for raising it. The centerboard is a 30lb of flat steel and is prone to corrosion.
These are really fun boats to sail, fast, forgiving and they have the wieght to stand up in a blow.