Check at the New York Academy of Medicine, on the east side of Central Park, about 105 street. Last time I was there, the library kept business hours only.
There seem to be at least 3 directories of American doctors that were published in the 1950s and 1960s: one by the American Medical Assn., covering the country, and two covering NY State only, by the Medical Society of New York and by the New YOrk State Board of Medical Examiners.
There are also directories of hospitals which that library should have.
The Academy keeps its material on the history of medicine in a special collections room, and this stuff may qualify as historical, by now. When you call, ask about access.
George A. Thompson
Author of A Documentary History of "The African Theatre", Northwestern Univ. Pr., 1998, but nothing much since then.