There's a chance a machine shop or fabrication shop may want it, but not at full price IMHO, even at a discount I don't know if too many shops would want it.
That's a lot of steel to just have laying around waiting for an odd request. I have drawn machinery bases in the past that used comparable size steel plate--BUT I also specify what steel to use, whether its M1020 or A36 or something else. When I place an order with a machine shop, the shop is responsible for getting the proper steel, so they almost always then order it directly from a steel supplier. That way they are assured it is the proper steel, clean without a lot of rust, of known origin, and they don't carry a lot of unnecessary steel in their own inventory. Many shops now will have have their steel plate pre-cut to the exact size in advance, saves them time and money ( a steel supplier with a CNC plasma cutter or waterjet or other such cuttter can do it cheaper, faster).
edit: In fact, let me state a little more emphatically: NOBODY should take a piece of plate steel, from unknown origin, and use it on a critical item--like say a bridge, or a critical piece of machinery. They can't be assured of its metallurgy, or whether it's been damaged; fatigued, for example--or even struck by lightning. I saw an I beam that had been hit by lightning, it was now very brittle and useless for anything structural.
Sorry, I calls em as I sees em, ain't personal at all!