This is an old sewer's trick. Use any separating zipper you have or purchase any length. Mark where you want the zipper to stop. By machine or hand, sew a bar tack (whip stitch if you don't know what that is) right over the zipper track on each side where you want the zipper to end. This makes a zipper stop so the zipper won't come off the track. Cut the excess zipper off at the ends. Sew it in your garment. You can also leave about an inch more than the length you want, fold the zipper strips over at the top, then sew them down, and sew them into your garment. I don't think they have metal zippers anymore. It's mostly plastic. You can easily cut the zippers with a kitchen shears or an old pair of scissors that you don't care about.