From all operating bases of Spirit and Frontier Airlines you can get flights to Haiti as listed below
Frontier
Spirit
Atlanta, Chicago–Midway, Chicago–O'Hare, Cincinnati, Cleveland, Dallas/Fort Worth, Denver, Las Vegas, Miami, Orlando, Philadelphia, Phoenix–Sky Harbor, San Juan, Tampa, Trenton
Chicago–O'Hare, Dallas/Fort Worth, Detroit, Fort Lauderdale, Houston–Intercontinental, Las Vegas, Miami, Newark, Orlando