One version of that piece of metal is a "Nicopress". Common in sailboat rigging though I think they started with telephone companies. Look for a boatyard that deals with sailboats. Call ahead to make sure they have the fitting for your wire size. If they have the fitting, they will also have the tool (which you will pay them to use, they won't lend or rent it out).
You could also try a full service hardware store. I haven't tries that option. Since I used to sail and have always lived close to saltwater, finding sailmakers has never been hard. Plus I have a small Nicopress tool. (Used to own a boat.)