Call Canon parts and see if they will sell you a screw. Then see if you can turn down the service. If you have the screw size and length, you might be able to find a matching one online at some of the camera parts houses. Usually, the screws are not just 5 cent hardware made in China like you find at Lowes, but you might check there. I buy up old cameras and broken lenses at garage sales, and, if I can't fix them, the screws go into my spare parts box and have come in very handy for replacing lost ones.