Actually, since we do not know the numbers.tjst are needed to construct say a mech, it is still irrelevant. Maybe a 30 ton Valkyrie needs 6000 tons of steel that are refined to the 30 tons of its hardened military level armour. Or not, or just the opposite. And green. We have no hard data, so hard data in other parts is just not that important.
we can get a real good guess, though. because steel doesn't work like that, in order to get different properties you alloy it with other elements, so you're not reducing 6000 tons to 30, you'd be taking the steel you need and adding other things to it, which means you're using less steel by a small percent.
it also wouldn't be 30 tons of steel in a mech. as there's more than just steel or even metal that goes into a mech like the armor glass in the cockpit and the high strength myomers of the actuators, and much of its internal volume is empty space.
assuming all standard IS equipment, a 30 ton mech is built on a 2-ton structural steel chassis. that's the internal structure. then you have six tons of armor, assuming it's standard armor that just six tons of armor steel. so that's 8 tons of steel right there. the standard cockpid is like 3 tons, with let's just say 10% of that is the electronics, armored glass, and the gyroscopically-stabilized refrigerated cup holder.
so that's 10.7 tons of steel right there. since we almost never use "pure" steel maybe about 20% of that mass will be various additives like chromium, molybdenum, titanium, nickel, etc.
iron and carbon being some of the most common elements in the universe it's not hard to assume steel remains the main structural building material in 3100AD.
6000 tons of steel can contribute to 560 valkyries.
i feel like the bottleneck in making battlemechs isn't raw materials, but that they are so very complicated machines and require a complex network of systems to function. so it's less the lack of material and more the lack of expertise that drives the cost and difficulty of production up.
but this isn't JUST about making battlemechs, but supplying raw materials to all of society. everything from steel to glass to plastics to copper and gold for electronics and everything else.