One of the first public art projects Alyson and I did was a bell that we put in our front yard.
Originally the bell was a small, scuba-sized tank that we found in a scrap yard.
We gifted this bell to Alyson’s grandparents (it now lives on their ranch in New Mexico), and got a new, larger tank to replace it.
If you are looking for a source for old gas cylinders, Thunderbird Cylinder in Tempe, AZ sells them. You can also sometimes find them in scrap yards, but those are both more expensive, and they don’t always have the primary valve removed, which makes me a bit nervous.