need a small boat with shower
Try using that head in the bow in a seaway and you might understand why that layout is so rare. (I suggest wearing a helmet should you try this.)
While not a student of boats with showers, you could install one of those telephone shower heads in any boat with a head. Put up some hooks for a shower curtain to protect the rest of the head and there you go. My Pearson 27 has such an arrangement, as do tons of other boats. The setup works, although it helps if you can dislocate both shoulders at once.
I don''t know if you mean a separate shower stall as well, but that will eat up a lot of space in a boat the size you''re talking about.....space you''ll need for better purposes IMHO.