Sadly, this true with 722.5 too-NO valve body parts are available too
I'm a DIY'er that wants to obtain every part for my car, but I have come across the 722.6 does follow the pattern of parts availability. Luckly, aftermarket manufactures(and mercedes) make parts for the valvebody. Chrysler uses the 722.6 on line-up of cars.
I like Mercedes Vehicles, and the classic car lines I like the W140 and the R129 are available with a 722.6. The 722.6 is a great transmission because easy to service(only 1/3 of the time required to service),it has high-output capacity.
Some in Europe is making a cheap stand-alone transmission computer for the 722.6 for use on older Mercedes'.
Martin