Just a few thoughts on making these springs. I have not tried making them with the slotted nail method, but I have made them in place using the recommended 0.016" diameter plain steel guitar strings.
Making them in place with the 0.016" resulted in springs that work. The problem is that these springs tend to be a little too powerful for the lowest idle settings. By lowest idle, I mean two or three clicks up from grounded or off. At this lowest idle, there is not enough centrifical force for the pawls to overcome the springs, and you can hear the sound of the pawls engaging. Not good.
So, maybe I need to experiment with some smaller diameter wire, more like the thinner factory springs. You can still find NOS springs, but they tend to cost between $5.00 to $7.00 each which is a little steep for me.