I'd like to know the number of practitioners of the following
specialties in the U.S.:
- Oncologists
- Dermatologists
- Cardiologists
- Orthopedic surgeons

In particular, I'm looking for numbers of these specialties who are in
non-hospital practices, i.e. independent practice, physician groups,
independent clinics, etc.  I'll offer an additional $20 tip if the
results allow us to discern the number of "non-hospital-based"
practitioners of these specialties.

Thanks!
-Roy