I am not certain if they can sell the local segment, but Air Jamaica Express flies from Montego Bay-Santo Domingo-Port au Prince. You may also want to check Tropical Air Haiti, which I believe serves the route with a Shorts 360. I don't know their web address off-hand, but you search for it off of Yahoo.com.
Hope this helps,
Brian
Actually...I just checked. Air Jamaica Express does serve the route 4 times per week (Mon/Wed/Fri/Sun).
