Carries a patch panel that replaces the part of the hood nearest the 3 vents, which is the most common rust area:
http://montehospital.net/shop/index.php?main_page=product_info&cPath=1&products_id=22
You cut off your rusted area and use adhesives to bond this to the rest of your hood. I have no experience with this product.
The other alternative is to switch to a fiberglass hood. I'm not sure if anyone is currently making them. If you are a DIY-er, you could clean up your existing hood and make a mold from it, then crank out as many replacement hoods as you want.
Pete