When a functional gable vent begins to deteriorate, it is often an inviting entry point for critters in your attic. You should inspect your gable vents each fall to ensure they are in good condition.
In the event you find some damage, most home improvement stores can order a new vent for your opening. These vents will be available in cedar, redwood or even a pvc.
You can visit the Awsco website to see what vents are available for your home.