Parts not available is a real sore spot for me. I have this exact ZW. One of my handles does not go to zero volts. But in my case the reset button is broken. I found the button piece of the reset button in the bottom of the styrofoam packing for the ZW and thought no big deal because I thought the only reason to use it was for a reprogram. Then when the handle wouldn't go to zero volts, my dealer gave me the bad news about the replacement board not being available. I was micro/miniature board repair certified years ago when I was in the Navy so I am sure I could replace the button or put something in its place but it's the point of it. Both handles broke on mine and I don't manhandle my stuff at all. Parts were still available at the time for that. IMHO when you pay the kind of money we shell out for this stuff, there should parts support for more than a couple of years.
For the handle parts that are not available it might be possible to get replacements 3D printed. I don't have a clue how to get a design done that could be printed but I've seen where this has been done for other stuff. If you can't find the handle parts, it might be something worth looking into.