I visited Dixon Tool and Die, Inc. today to see about having some machining done.  Bill Dixon Jr. was very helpful, and explained many of the points that will make the process go easier.

1. Design for available parts and sizes
2. Buy everything you can stock (pins, springs, aluminum channel, etc…)
3. Minimize milling by doing the above

To that end, I did a bit of springy research, and found that neither McMaster Carr or Manhattan Supply Co. had really small springs in bulk (only precision (eg expensive) springs in those sizes).

So I re-placed one of the pins to fit a standard (cheap) McMaster spring, and got pricing from http://centuryspring.aitrk.com/products/extension.html for a special spring.  The trigger spring has ~ a 2/1 leverage (finger/spring), so we need to have several lbs of spring pull to equal a decent trigger pull.  They have a spring with these dimensions:

While $1.20 is more than I wanted to pay, it sure beats $2.00 to $3.00 per spring that I was looking at from McMaster.

With a shorter spring, I was able to re-design the pin placement, which resulted in this: