I was never aware of a windage-adjustable Weaver extension type ring, but there have been straight up windage-adjustable rings that work on Weaver and picatinny bases. Millet's website doesn't even list rings anymore, and I don't know when they stopped offering rings. The only Millet rings I've ever seen in use failed so I was never interested in using them. They did offer the Angle-Loc ring which is windage-adjustable and I think various merchants still have some in stock. Weaver also offers a windage-adjustable ring that works on Weaver bases and picatinny rails.
If you can find a picatinny rail that would work for your rifle, you might be able to accomplish whatever you're trying to do.
If you'd reveal the type of firearm and scope you're working with, you might get better responses.