Are you saying it was there because the parking brake worked okay or because you remember seeing it?
Some have a spring on the cable under the vehicle, though I don't necessarily mean that's the only one and if there are two it's probably not the one to return the pull shaft to the inward position.
If there was a spring on the release lever shaft, you might check whether the end of that shaft comes off the piece it hooks into in the rear or is pressed in, in a way where it could be a problem trying to get it out, put a spring on, and put it back in.
AFAIK the entire thing is sold as an assembly, no spring sold separately. That spring being coiled around the shaft (if present on your vehicle's design), I don't see anywhere it could go except sliding to the back of the shaft if the stop/piece on the shaft had broken off. If the stop on the shaft isn't there then you'll need to add something to do that, maybe welded on or a little hose clamp or ???
Then again I could be wrong, could be thinking of an older generation. This seller shows a different spring /assembly setup but the compatibility details only go back to 2005. Anyway if yours is set up like that, the pic shows where the spring on it is and it is a listing for just the spring: