Screen Plungers (?)

Dear Swisco,

I have a screen that is missing one of these plungers (I assume that's what it's called). The hold the screen on and preventing it from coming out of the frame. The black plastic piece in it's lowered position (first picture) locks the screen in by allowing the plunger to extend out of the through hole. When you pull the plastic piece up, it retracts the plunger and you can then pull the screen off.

Anyway, I need one (would like to buy several to have on hand) at least of these plungers as I cannot find them anywhere. Thanks!