I was also wondering about that -- not only the small 25 lb tanks for the BBQ, but what about the availability of propane delivery for a large tank (100 lbs or more) at your house?
Depending what part of the island you are. I'm not sure in the metro area, in Guayanilla, there is a place that will refill any size bottle. Most towns will have one or two business dedicated to deliver propane. Prices are regulated by the government.
Articles to help you in your expat project in Puerto Rico