Go to a website for the nearest hospital/health care provider service.
Find the department you are interested in.
See if the physicians' emails are listed online (they usually are), otherwise, find the admin assistant email.
Start sending out emails and detail exactly what you want - say you are an undergraduate student from X, and that you would like to find out more about profession Y. You were wondering if they may have B number of minutes (usually 20-30 for this kind of thing) available in the near future to talk to you. Thank them for their time and consideration.
Wait
If no response after a week, email more people.
Don't email too many at once, you don't want to be stuck with too many people who offered to give you their time.
If you don't give some broad times you are free in the initial email, then you better take whatever time the physician gives you - this isn't a time to email back and forth to find a time/date that works well with your schedule.