The metal FO sight off of my Diana 240 would be a close fit: ***snip***The rear screw hole would need to be elongated toward the front about 3 mm, and both screw holes would need to be re-drilled for the Optimus screws. If you don't want the FO, just paint with black nail polish. Other than that I believe there's a Williams peep sight that may fit, but unfortunately I can't tell which one.HTH, and good luck.