Large RV dealers with a large service department sometimes have Propane refill available. My local one does and does a brisk business on the weekends refilling tanks. I even take my 20 lb ones up to refill as I don't like trading in my tanks anymore until they get some age on them.
Actually used to trade all the time and got stuck with one that was over 10yo that the place that gave it to me (local) wouldn't take it back the next year when I finally emptied it (It turned over the course of about 5 months). I was top ten ever ticked off!