We have a local sign company that gives that material away. You have to check once a week, as it is a hot item.!! We have some Amish in the area, and they get the large one's, and cut them down to make smaller ones. They have the HD sewing machines to sew the edges, and the eyelet tools, so as to make tie downs.
Our horse club got several a few years ago to cover some lumber we salvaged out of a building. Lumber was covered for 3 years, and tarp was still in good shape..!! The sign company is more then glad to give them away, saves them on the disposal fee.