Consider looking at motorcycling rain gear. They will be easy to find in stores and online and will work great for bicycling as well. While bicycle shops may not have a "rain gear" section, motorcycle shops usually do.
Good bicycle rain gear will be properly vented; motorcycle rain gear may not be. it's an important design consideration, because you're going to build up a lot of moisture inside from the physical exertion of bicycling. Any bike shop worthy of calling itself a "bike shop" should have rain gear, or be able to order it.