You have to be careful assuming that old tools/springs are a particular steel. That's why I buy virgin steel
In this country springs are made from EN45 (silicon manganese spring steel that is nothing like L6 chemically), EN43, EN42 (like 1075). Saws are also made form L6 (though our L6 is very different to the US version), EN42, EN47, CS70 (1070), CS80 (1080) as well as the rubbish steels. Each steel needs to be heat treated in teh correct way for teh chemistry.
Most modern leaf springs in the UK are EN45 or EN43. 45 is great, works and uses similarly to 5160 (which you can't get in this country sadly), but EN43 is too low in carbon for an edged tool. Great springs aren't alwyas great knives these days I'm afraid. Also as Longstrider says, most of the springs here are a bit thick without a power hammer (or patience in my case!) so maybe an industrial bandsaw or a large circular saw (eg from a saw bench on a tractor) would be better for you?
If you use old steel, spark test it. Basically touch it against a bench grinder and look at teh sparks. There are pics of this online I'm sure. It's a crude guide but it gives you an idea of whether the steel will likely make a good blade. Then take an offcut and try some heat treating experiments with it just to make sure it will work. It will save a lot of time and tears doing that! I nearly made an axe out of a fork lift truck spike a while ago. The thing sparked like a medium carbon steel (as expected), got hard on quenching, but at a very low temperature the hardness rapidly dropped off. So it could be made hard and tough, or springy but would never hold an edge. Experiment!
If you struggle with finding anything send me a pm of teh dimensions you need and I'll have a dig about and see if I have anything suitable
