Is this a new SA three speed or an old one? I was assuming new based on your use of the SA site, but you said Hercules. I'm confused. For all things old-three-speed related, see Sheldon's site:

http://sheldonbrown.com/english-3.html

Harris Cyclery (for whom Sheldon works) sells lots of 3-speed bits.

Once I know if it's old, I can help. If it's new, I can't.