I have made them by using a fender washer (try to find a thick one) and reaming it 3/4 the way through the center hole, with the same size as the clock shaft, You will need a reamer to do it.
Using a punch, drive the sides of the center hole to give them the flat edge you need on the side. You may need a set of jewelers files to clean up and fit tight.
Then drill & tap your hand holes for #6 screws.
Hold the washer w/ vise grips when drilling & tapping the screw holes.
something like this.....