Look for Haulmark, the trailer manufactuer people, (I know they have a location in PA) and try to get one of the employes to snag you some diamond plate scraps. They also sometimes sell their scraps for the same price the recyclers give them. They regularly scrap out LARGE pieces of Diamond Plate. You could also just call them up and find out who they use as a scrap recycler and then call them up to buy scrap.
I sell a auto feed screw system to these guys and I regularly walk out of there with a few peices of "scrap" I have gotten pieces as big as 2' x 8' before.