You can replace any steel spring with another that has exactly the same coil diameter, wire diameter, pitch (the distance between turns) and free length (the length overall when nothing is touching it). Alternatively (and much harder to do) you can stretch and contract your old spring until it has the right length and constant pitch, then re-harden and temper it. If you search through a box of springs (available in hardware and tool shops) you may find one that is correct except for overall length - you can then cut it off to suit your application. Usually you have to mildly soften the last couple of turns on each end and collapse them to give the correct ends. Of course you measure the free length after you do that not before.