Roadside Scrap Drop Off.

I would still try it, maybe don't weigh it. Heck some people could just give you the metal vs going to pay to dump it...

The idea isn't a bad one, just if your not with the trailer your prolly gonna get a trailer full of the stuff the landfill doesn't accept. You would prolly be better served to find a new construction site and speak to the contractor owner or foreman, they may let you park your trailer next to the roll off boxes for the metal to decrease their dumpster weight. Provided they don't have a box for scrap metal