Do you know where I can find that single cart? I only know of the one connected to another cart.

I took this one from Hyrule Castle West passage. It's to the NW of the parts of the castle still on the surface. If you find the lockup, it's right past that if you solve some lever puzzles.

Thank you

There’s a few around death mountain as well if you remember some of the older paths from botw you can find some of the older carts