There is still a boatbuilder near Monroe,WA who has the Clark Boat Co. molds for the SJ21, SJ23,SJ26, SJ28, & SJ30. I know he makes duplicate rudders, tillers, etc. for these boats plus has access to other rigging used on these models. He was still building them ten years ago when I visited his shop. The SJ fleet in Seattle will have some further info - I expect.
Congrats on owning a good sailing boat.