window screen retainer

Our condo complex is 40 years old and these things mount on the window jambs to keep the screens in place. Most are broken off and the rest break very easily. I want to replace them, since screens occasionally blow out of the windows and end up in the parking lots when it's really windy. I can't seem to find a) the proper name for this part, and b) the part itself.

I need your help!
Thanks big,
Melissa