Simplex Retrofriction bar end shifters are nearly impossible to find. I've only seen three of them and I bought them. Look for the notch in the back of the lever that holds the end of the spring. They look identical to the standard Simplex bar end shifters, otherwise. at least until you take them apart. Beware of missing locknuts. I think that you are correct that the cable pull would work well with a Huret derailer without the demultiplicator.
A Campy Rally or Shimano Crane will work on your hanger if you tap it.