You can find a listing of disabled travel specialists at http://www.access-able.com
by looking for travel agents in their database. Some of the agents listed handle cruise bookings.
Note that each of the specialists I know either doesn't charge or charges minimally for handling shore tours for clients whom they have booked on cruises despite that setting up the tours are often time-consuming and noncommissionable. At the same time, most (if not all) either won't handle these types of details for someone who didn't book their cruise through them or will charge hefty fees. If you booked directly with a cruise line and have not yet made your final payment, you might want to have a specialist "pick up" your cruise booking from the cruise line. That way, they can be stay on top of the accessibility details for you, watch for any new pricing promotions which might come up *and* take care of the shore excursions for you.
Any way that you handle it... have a wonderful vacation!