As Kostas mentions, a suitable tool is not to difficult to make.
4 evenly spaced 3,0 mm diameter pins on a circle with a radius of 17,5 mm gives the tool to do it.
I made a 20 mm hole in the middle to push a large bolt through. The bolt can be used to press the pins of the tool into the nut. Not required on new rings but as you say they are usually damaged by hammer and punch.
