Try going to the nearest Department of Economic Security or the agency that provides Medicaid. They can direct you to a website that lists clinics in whatever state you are in or need.
If you have insurance you can go by their list of doctors and associated clinics. If you have no insurance then not all states have the same medical agencies for example Scripps and Kaiser is only in California. You can always go to a large university hospital. Best to try a friend who knows the area that you are going to. I don't believe there is a network across the US that is connected.