These 2 web sites have small prop planes. https://www.timair.net/ and www.intlairlink.net

Did a search and came up with this:

https://us.jetcost.com/en/flights/ja...gril-kingston/
Recent flight searches Negril - Kingston
Flight Airline name Price Type Trip dates Search date Provider
Negril - Kingston Interisland Airways $116 Round-trip 31 to 31 August 144 days ago
Negril - Kingston Interisland Airways $56 One-way 07 August 193 days ago