Sorry that I did not see this before you left. I just returned from a cruise which stopped in Montego Bay. We contracted a taxi at the port and put my scooter in the trunk. We requested to be dropped off in the city center and then made our own way to the fort and flea market. We then went down the main street which we were advised not to stray far from. We did deviate over two blocks to see St James cathedral. We only saw the outside. We had to shake off several locals who wanted to be our "tour" guides.
I saw the poor side of town and a small shopping center. My friend went to Margaritaville (okay for w/c) and Doctor's Beach (definitely not a place for mobility chalenged). My friend did not climb down the many, many steps to get to the beach.
Here is a source for w/c van in Jamaica. Ken's Wheel Chair Service for airport transfers, sight seeing or?? RENVILLE SYMTHE cell: (876) 772-3631, office: (876) 956-5450, fax: (876) 609-4408, e-mail: firstname.lastname@example.org
I hope this is useful to someone else.