Product review (3 stars): Plastic knobs, wish there were metal substitutes.  Ordered from GE
Read the reviews for WB03K10303 and called the GE consumer number at 800-386-1215.  Amazingly good service.  They also quoted a price of around eight dollars so I bought 4.  I asked if there were any metal substitutes for the knobs and they didn't have any knowledge of them.  My three star rating is for the knobs themselves, which I imagine will break again soon.