Hi, Vincent. You can get pressed tin as used on ceiling from several sources. Check the ads in magazines like "Old House Journal". You can get flat tinplate or smooth rolled galvanized from metals warehouses. Just a thought, but you can also get copper the same way. Old signs are available from antique stores and are liable to be rusty and pricy.
As a matter of fact, about any way that you put up tin walls is likely to be pricy. Getting it in flat sheets will probably be the lowest cost. I'm sure that you will want to put up drywall as a backer before you cover the walls.
Good luck and perhaps others have some ideas on this. Henry in MI