I don't know of a source, but have you considered the heat buildup issue associated with metal containers?

Maybe you have a solution in mind, just thought I would toss it out if you hadn't considered it.

I too have the heat question in mind.
Why metal. Perhaps you prefer the shine of copper or other metal.

If the pot in question has real copper finish, it poses a problem of oxidizing with the use of water and fertilizer.

The 8 cubic feet of soil would constitute a very heavy container--if used on a deck, hopefully it could stand up to the weight....soil and water.