There are a few J/30s posted on the
Boats for Sale section. This has specific boats, and a post listing
Other J/30 Sailboats for Sale. Some of these have been recored in areas where there was wet balsa, so the hull integrity is good. I suggest you contact the owners and ask questions. Post some questions here too on a general nature to help your search.
You just missed out on
Preparation J - a west coast boat that sold in July.