Map Camera in Japan is now selling the new version 2 lever-type thumb rest for Leica M10/M10-P cameras (similar to the lever in the Leica M10-D model). The price is ¥49,500 (around $430 including tax).
Information on the previous version 1 can be found here:
Lever-type thumb rest for Leica M10/M10-P now available for sale
