When my rudder pin failed and while waiting for the replacements to arrive, I made a substitute out of a section of 3/8" plastic clothes hanger. The top was drilled to accept a split ring. The bottom was grooved to make two nibs similar to those on the Hobie pin. These were bent outward with a hair dryer and pliers to keep the pin from riding up. The pin was installed from the bottom and then secured with the split ring. When my original Hobie pin failed it was the nibs that broke off. The pin then twisted out of shape when the mounting twisted up.
The plastic was cheap and available, hanging right there in the garage. Shaping the nibs provided a point at which the pin could fail instead of breaking the drive mounting as would likely happen with a metal pin. The difference in physical properties between nylon and plastic did not appear nearly as important as providing a shear point with a reasonable amount of flexibility. In any case, the Hobie pin was installed as soon as it arrived since the purpose was to keep sailing and not to test my design skills.
The plastic clothes hanger pin was also suggested by another contributer to this site but, as I recall, their pin stuck out below the rudder mounting and was fastened with a screw or bolt.