Coil spring with strut, or a leaf or V-spring design? I have two cigar boxes full of hammer, sear and mainsprings for both boxlock and sidelock guns- fotos of the broken spring and the unbroken one would help-- You are 100% right- just as with a garage door set of tension springs- if one fails, replace both with new ones as a set- a "matched pair" as it were.

"The field is the touchstone of the man"..