Hi, all.
Not sure how helpful this will be, but for those visiting Okinawa and interested in visiting Tokashiki or Zamami, etc., you can do this yourself by taking the ferry from Tomari Port in Naha, but on another travel forum, someone was asking about tours. My Okinawan cousin responded with this site--but it's in Japanese, so you're relying on google translate.
https://keramatour.world-tours.jp/

Googling for a charter boat, I did see this company, but have no personal experience with them. https://seadraggin.com/

or in MS Edge browser, right-click and choose Translate to English
lots of fun stuff

Wanted to post some additional info here in case others were looking.

For public transport from the airport, there is a monorail that goes to several points around Naha, to Kokusai Dori (International Street) to Shuri-jo (Shuri Castle), and other shopping destinations (duty free Galleria, etc.) Online brochure is here... https://www.yui-rail.co.jp/navi/

Or for those wanting a longer stay at a resort up north, there is an airport bus that goes to several resort hotels up north. Even if it doesn't stop at the one you want, they may be clustered together somewhat, and walkable. I know that is the case at the Chatan/American village hotel.
https://japanbusonline.com/en/CourseSearch/14700010001

ChgoGal - thanks for the info about Okinawa. I am going to Naha and Ishigaki for a few days during my time in Japan. I looked up the date that huge cruise ships will be there and luckily only one day coincides with my visit....and the airport bus also goes to the Aquarium which sounds great!!

HI, Mara. Hopefully the bus schedule expands. I'm a little confused by their schedule. It doesn't seem to go to all their stops in Feb/March. Hopefully, you can find info for the Aquarium on the date you want. There's also google maps, but it seems the airport bus would be more "express." Good luck!

Actually, I think this is the bus line I'd looked at for my trip last year, but we ended up being driven around by my cousins. https://okinawabus.com/en/ls/ls_timetable_fares/

https://www.okinawa-shuttle.co.jp/en/timetable/

This is the one I found but of course, I will double check everything when I get there in April.

Thanks, Mara ! Even more options, it seems. Have a good trip!