Hi Goat Herder,
I've been on the same quest for custom length 12, 11, or 10 GA. spokes for months.
From what I have been able to learn: And this is certainly not complete, (maybe someone else will chime in).
1) Some bicycle shops have a simple little hand operated machine that will clip and thread roll 14 & 16GA. spokes to any length you need.
2) Custom MC shops have the same set-up...but they don't do the small stuff!
3) The 12 & 11 GA. spokes are impossible to find in custom lengths.
Jim