I would be inclined to take the lazy man's way out. Locally we have a spring shop that appears to cater primarily to the automotive industry. They also however carry a large selection of small coil springs. Just take a set of dial calipers with you to the local equivalent shop and buy a spring with a little thickner diameter wire and of course with inside and outside dimensions that will still fit in the space alloted.
Referring back to your original problem, I find myself wondering if your problem is not spring strength but friction and if something is binding; bent firing pin for example or simply crud in the hole.
cheers Doug
