I got a free one from Depot. They must have just refilled the automatic cages and forgot to leave a few open slots. So it opened for me to put my empty, and there was a full one in there. Took it, then it opened another cage for me to take another one. OK.
One other small thing. Many propane tanks have a plastic wrapper around them.
Rip it off. All it does is collect condensation and rain water, holding it agains the side of the tank causing rust.