Large Builders bags (Micklefield HP13)

Hi,
I am looking for used, but intact builders bags. I volunteer with Chiltern Rangers and they use these as drag bags to remove brambles and other arisings when they clear paths and scrub to create habitat for wildlife. As you can imagine , they wear out with being dragged back to the van. It would be great to have an ongoing supply of the bags. They are usually thrown away as the builders merchants wont reuse them. I arrange to collect from around High Wycombe area. Please contact me if you have any. Thanks in advance Regards, Sue