spring steel ?

The whole point of A36, as I understand it, is that it is essentially unhardenable.

That can be either "the side of the road" or "the auto junkyard", or your friendly neighborhood independent mechanic. The mechanic can be easiest, as he's generally already pulled them out of the car, as opposed to you having to do that at the junkyard, and he's throwing away the generally larger pieces that stayed in the car, as opposed to the smaller ones that fell beside the road. Might cost you a six-pack of beverage of choice, might not. Coil springs for round stock, leaf springs for flat stock. Forge them enough to find any hidden cracks...

A36 is a generic mild steel. Does not heat treat. Period. 5160 is a mid range carbon (.56% to .64%), low alloy steel that will heat treat to a midrange but not like the high carbon spring steels. If you need 5160, keep looking.

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