No one sells those clamp on AI "notches", you have to custom make one for each lens, as the length depends on the max aperture of the lens. Those older lenses have a threaded aperture ring and are not thick enough to catch the AI tab when machined, which is why someone made that small extender piece.

Edit, you still have to machine some of those rings so they don't run under the AI tab and stress it to the point of breaking.

2nd edit, and the machined notch on that one should run way to the right, it wasn't done properly.