Here is what I did after John (the customer service rep at Wolff Gunsprings) responded to my first email:
I took pictures of the original springs, with caliper measurements (overall length, outside diameter, inside diameter and number of coils per inch) and sent them over. He sent me a bunch of spings to try out that met the physical specs, and a couple that didn't (longer, but less coils per inch, so compressible to fit). He even recommended cutting off coils one at a time until I get one that fit.
Basically, I was doing R&D for them for free, but I don't mind because it got the pistol working how I wanted it.
They'll work with you, if you can give them precise information.
It's worth a shot. I mean, what have you got to loose, right? The Sigma's not gonna get better by itself.