I just opened a phone book and started calling doctor's offices to find someone willing. If you're talking about in a hospital and not private practice (like I did), you'll have to talk to the hospital - some won't let you because of privacy issues.
Usually you meet doctors during your clinical activities and eventually ask them.. You could ask your personal physician. You can ask if they have a program through your pre-med office to match you with willing physicians. Last choice is cold calling, as mentioned above.