Window Screen Clips (?)

The part is used to secure the window screen in the window frame. It is made of plastic and is 1 1/2 inches long. The windows in question came with my home when it was first built, and date from 1993. They were manufactured by Empire Pacific Windows, which was acquired at some point by Cascade Windows. Cascade was no help in supplying replacement parts, but they did give me your web address. Do you have any idea where I can purchase some of these parts? Thank you for your trouble.