I am not personally aware of such a list, but for the second question it does depend on the specialty. Some specialties require a certain primary residency before obtaining a particular fellowship (for example, if you want to be a cardiologist, the only pathway is by completing an internal medicine residency first followed by a cardiology fellowship). Other specialties feed from multiple different specialities (for example, if you want to be a sports medicine specialist, you can pursue it by family medicine, internal medicine, pediatrics, emergency medicine, PM&R; you can do a sports neurology fellowship from neurology; you can do an orthopedic sports fellowship from orthopedic surgery). Other specialities are either you match into it first as a primary residency or later do a fellowship to get that position (for example, plastic surgery. You can match directly into plastic surgery as a residency program or you can pursue general surgery and do a plastic surgery fellowship. These options are becoming less so, as far as I understand, considering plastic surgery, IR, and vascular surgery are now integrated residency programs).
What subspecialties are you interested in?
