Where do you find which disorders have service dogs available for helping people?

Start with Google. Service dogs are used for many reasons. I've seen them used with people with diabetes - particularly people who become hypoglycemic (low in blood sugar) without warning. They can be used to warn patients of oncoming seizures. Certainly, they are used in anxiety disorders or with people who have visual loss. In our state (washington) there's a service dog training program in a women's prison.