Hi Doug,
The company I used was:
http://www.southernsprings.com.au/
Its almost been two years sinceI ordered mine but you can try to get in touch and request the springs they made forGreg Hupeden. The springs thatI have used take a loading of around15kg and there are two springs which seemed to be effective...
1) 1.6mm dia x 20 coils (used on my jet)
2) 1.6mm dia x 19 coils
Iwould suggest getting both of these made up and choosing the one that feels right for your jet. Hope this works for you.
Cheers
Greg