Here is the website for the current Mystere 4.3 owners group: https://groups.yahoo.com/neo/groups/mystere43/conversations/topics/629
(you have to become a member on Yahoo to join in)
This would allow you to contact current members and ask questions or advice.
Here is the former website with lots of info and easy access: https://mystereowners.wordpress.com/
This provides history of the U.S. class and lots of useful info even now after years of non use.
This is the website of the manufacturer: http://www.mysterecomposites.com/index.php/mystere-catamarans
The boat is no longer made but they can provide parts and advice.
That should give you a big start in learning more about that wonderful little boat!