Sorry to repost, but I just reread your post, and saw that you're docking in Montego Bay. That being said, I'm not sure if there are any tours that go to Dunns River Falls from there. When I was in Jamaica we docked in Ocho Rios.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)