Little string inside shifter is broken. What should I do?

[jeracravo]

Hi everyone,

I have a Trek 7000 (93/94) still with tons of original parts on her.
A few weeks ago, the rear shifter broke, not shifting to the lighter gears, but was still shifting to the heavier ones.

When I opened it, I saw that a little spring inside it was broke.

Just like the one seen here:
http://www.cs.hmc.edu/~geoff/deoredx/reductions/P2004.09.08-12.00.07-3849.01.html

I can't find this spring anywhere. What should I do?

Is there a specific name for it?

Those are the pictures of the actual shifter and rear derailleur.

Thanks for any info you can share.