Where do you plan to go?
I know the Virgin Islands was no problem and Puerto Rico no problem, the Bahamas depends on where you are. Grenada I could find it also. You might have to do some looking around but I have found propane just about everywhere there is a big town, I was in Bocas del Toro about 15 years ago and had to take a ferry to Panama to get it.
I might have to hire a taxi or catch a ride to get it but I usually had no problem.