Try doing a Google search for each port that you are going to. Most of the ports have a website and usually many links off of them with things to do, ship schedules, etc. I don't have any in my favorites, but I have found some in the past.
Most of our cruises were Eastern Caribbean, so I was probably looking at St. Thomas and St. Maarten. I think most of them do, with the exception of the cruiselines private islands. They don't usually have them, although NCL did when we were on it in 2001.