Know a anyone with an old shed/barn they're getting rid of?
I used boards from such almost 30 years ago when I wanted to clad a new shed in a way to make it look older.
Almost as long ago I was helping build stuff on a hippy farm in New Hampshire and we clad one building in wood from a salvaged grain silo. The windows were all random salvage too. It ended up looking mint - rustic Bauhaus.
If you have the tools it might be better to get friendly with local parks maintenance / tree surgeons and cut your own, and either use it green or wait a year or two.
Know a anyone with an old shed/barn they're getting rid of?
I used boards from such almost 30 years ago when I wanted to clad a new shed in a way to make it look older.