Shamus
May I ask why you want car leaf springs? Is it for a project for your self or to make into something to sell? I agree with a few post Why by any questionable /fatigue /old worn out ones? If I just am screwing around for myself ok but to use used metal for a resale puts that object at risk my be of failing where new metal not that costly.
I do use train,car truck springs ,chain saws, wire rope and all kinds of good metal but only for myself or art objects. For knives id never use used . It is just the way I do things. My motto is it only cost a tad more to go 1st class so why cut corners on materials ?