You can buy a brand new one from Petro Nuts at www.petronuts.com
or you can troll the internet looking for an original.
Originals are available in clear, blue tint, and smoke tint.
You can expect to pay $400 to $600 for a clear and $600 to $900 for a color tinted cylinder.
I have a blue tint cylinder for sale at $800, but I will not ship.