Spring loaded clips to hold screens in place
We carry a bunch of different clips that may serve the same function as the one you're showing, but I can't really make out what you have from this photo. Is there any way we can see a picture of yours out of the frame? If we can see one that's undamaged, that would be even better. Please also provide any measurements you can.
If they aren't removable, I'm not sure how you'd be able to replace them. The only parts we have that come to mind are our 70-008 and 70-009, along with the plain nylon 70-195. See if you or a screen repair person can install one of these type on your screens. You might need to contact Milgard to get the same one, if they are still available.