Try and automotive or truck spring shop for 5160. I'm not talking about the brake, lube, spring and muffler shop. I'm talking about the place that supplies the spring shops.
Not sure where you are from but in our area the comapny is Standens Spring. An auto wreckers might be a possibility too - but you'd have to start by straightening it and annealing it.
Not sure about the O1 - does Admiral have it in your size?
Rob!