Hmmm -- Old Man Winter is shaking the house, so I'm stuck here ....
A clearer view of the spring (looking up from under the bed). Followed by measurements with the spring removed:
The body of the spring is about 1.40 long x 0.16 diameter, made out of 0.024 wire.


The overall length is about 1.68 or so overall.

The length is such there is little stretching when the actuators aren't squeezed, it seems that may make it pretty easy to pop off if it got poked with something. (But it does make it easy to take off or put on with heavy needle nose pliers.)
Then a suggestion for a crude and cheap replacement shown next to the B&J spring, the spring of a ballpoint pen refill floating around here.

One could bend the last loop down at each end and stretch it across. Most likely far from optimum, but might be better than none.
Ace Hardware stores (at least here) have an aisle with assorted and sundry hardware in compartmented boxes on pull-out slides; can't remember if they might have small springs among the goodies.
Another temporary semi-fix might be a rubber band or 'O' ring sized suitably to stretch across there, although it might interfere a bit with the lever that locks the front shift slide.
(Have fun!

)