I tying to find, “un-finished” BASSWOOD that is 1/8" thick by 8", 10", 12" x 24" wide, or similar sizes that we can use to build architectural mode.
It can not have a finish “clear coat” of any kind on the board, they do no glue together.
Try searching the forum for “hardwood source”, you’ll find a lot of options.
You’ll quickly run across ocooch hardwoods, they carry basswood up to 8" wide.
It’s possible that nobody will have anything larger without it being a glue-up. Generally speaking, prices climb rapidly per square foot as boards get wider, so you might be better off doing your own butt joints and glue ups.
Basswood plywood is available in craft stores as 12"x 24" sheets under the Revell brand. Considering that keeping pure wood from warping or splitting in such thicknesses you might look at Baltic Birch that Ocooch also has.
For extra thin plywood, these guys have it to 1/64" thick