I have no idea where you could find one. I have one that came on one of my machines, but I stopped using it. I found it was easier to just remove the tool head and flip it over to empty the powder magazine.
I use a "hairpin cotter pin" to retain the lower link pin. Just unhook the tool head spring, press out the taper pin, and pull out the lower link pin, and you can pull of the crank shaft assembly and tool head in seconds.
While you have it apart, its not a bad idea to remove the thrust nut and clean up the floor base and primer assembly.