window frame plastic plugs

Each of my windows have 4 holes in them, where the plunger for the screen inserts into the window jamb. There are 2 at the top of the window and 2 on the jam - 1 on each side near the bottom of the window. Each of these 3/8" holes is supposed to have a plastic plug in them. The plunger for the screens goes through the plug.
Over time the plastic plugs became brittle and broke. I need 100 of them.