Interested in a specific specialty? Try looking up the national association for that group or look at state-level work/labor force reports if interested in a specific geographical region.
This page lists AAMC resources about students and residents, institutional operations, and published reports. Much of the data is subscription based and therefore not accessible, but some reports are available freely online.
For the Medscape Women as Physician Leaders Report, Medscape surveyed a total of 3285 female physicians across all specialties to find out about their participation and interest in leadership positions.
A survey by Medscape that includes information on two important aspects of a physician's personal life that could affect treatment: burnout and bias. Over 15,800 physicians responded from over 25 specialties.