If you're set on replacing the cable stop, there are a few clamp-on stops available. These will only work if your top tube is round and matches one of the available clamp diameters, so first measure your top tube's diameter where the stop goes.
bikeparts.com stocks a few different clamp sizes (28.6mm, 31.8mm, 32.0mm, 34.9mm, 38.1mm).