If you are inquiring about the propeller shaft, i would suggest trying the Beneteau USA website. There are parts drawings on line, but I don't recall if there are drive train parts shown. Contacting them via email could possibly provide a lead. At least they could provide dimensions for, lengths,thread sizes, tapers, etc. that a local machine shop could use to duplicate a part.
If you mean the tail shaft of the transmission, then you would need the parts supplier for the particular transmission brand.