Getting ahold of industrial/factory window frames destined for scrap?

I was curious if anyone has ever came into possession of any of those common metal/steel, gridded, industrial window frames. I very much associate them with chicago, and I’ve been wanting to build a greenhouse. I drove by a few of the scrap metal recyclers on the west side, but only saw piles of smaller metal scrap through the gaps in the fences (though I swear I’ve looked out the window riding the west branch of the green line and seen some stacks of them). Does anyone know where I could get my hands on a few of these, preferably paying by the pound as scrap? Or anyone with experience talking to a crew demolishing a building and asking to cart them away?