Just ask a dr. you work with or that you know well, whether it be family friend or friend of a friend or you could randomly call a hospital. Some emergency rooms are familiar with people wanting to shadow and can set you up with a doc. A friend from college worked in a small clinic so that he could observe the dr. when he wasn't busy with his work. Don't be afraid to ask around. In my experience, people were excited that I was interested in their work and were happy to show me what they did.