Two ideas if you do not find a key, although that is the best idea. I think it is called a gator socket. It has pins that slide in to fit most any bolt. The pins might fill in the key slot. Second idea is the mother of all vice grips. If there is room, I know this was rumored to work for less than honest folks in the 80's to break locks loose. No one came back to the parts store saying it did not work. I think they padded the CCW side of the Vice Grip with a shop rag to not mess up the rim.