Most of the things I can think of involve a bender or brake.
As above, you could make a triangular shape with tabs on 3 sides of it.
If I made my own I'd probably bend 1/2" rod in an "L" shape and then weld in the diagonal brace. Square/keystock would also be different looking although I don't have that.
Eventually you'd have to get down to some deck screws or other fasteners to hold it to the wood above.