You can find blood oranges in some specialty markets, usually December through May. Many grocery stores now carry blood oranges in the produce section, sometimes loose, other times in packages. If your local grocery store or fruit market does not carry them, I would try Whole Foods or Trader Joes for your best bet in finding blood oranges.
Blood oranges are great for salads, adding amazing color for a simple salad. They are often used in juices and also in cocktails. It has a very sweet flavor and is complementary to many dishes.