Agree with checking with your own doctor first. If you're uncomfortable you can do a little lead in/fishing and just say you're looking for physicians to shadow and do they know of any docs that might be open to it.
The other option is to try to use your volunteering position to network and meet physicians to shadow. This can be a goid route because you've usually got some HIPAA training and that removes one potential roadblock. If you don't have direct access to a doc, you can observe who you do have direct access to that does have direct access to docs with a good relationship, say a nurse you work with. Be good at your volunteering, have pos interactions with the nurse, then ask if she thinks there might be a doc you can shadow.
There also might be some atypical routes you can use. For example, my local hospital didn't really have an (official) option to shadow doc. But it did have an option to shadow health professions (included a bunch of things except docs). I decided to do it anyway and it was pretty neat and informative. I shadowed a floor nurse, a histotech, a rad tech, a dosimetrist, met a medical physicist, and oncology nurses at the infusion center. I was respectful and showed a genuine in learning about each of these paths. When I mentioned I was in school to be a clinical lab scientist but thinking about maybe going to medical school after working for a bit the following things happened:
the floor nurse told me to make sure to treat nurses nicely, and i said my best friend was an RN and that I was pretty sure after being an allied health worker I wouldn't have trouble treating them with respect, she said good point and asked tried to hook me up with a doc to shadow, but the resident was elsewhere during my time there
The histotech hooked me up with a pathologist who spent an hour talking to me, then gave me his card. Another pathologist popped his head in and asked if I wanted to look at some cool stuff and we sat at a two headed scope and looked at a breast biopsy, a pap smear, and a lung biopsy together. He talked to me for quite awhile as well. It was pretty awesome.
i had a really great experience with the oncology nurses, had some lengthy discussiins about the specific challenges in their field. Then they told me I should meet the radiation oncologist and after he got done with his patient, he took time out of his busy day to talk to me about his field and gave me his card if I had any more questiins or wanted to come back another time.
Lastly, I did a research associate program in the ED of a big county hospital. This was a program designed to give pre meds exposure to emergency medicine while providing the dept manpower to do clinical research studies. Premeds get volunteering, direct patient interaction, and get to observe docs and docs get free 24/7 labor to interview patients and take down data. Plus we got to go to their thursday morning conference and occasionally other docs would pull a student and say "hey you want to shadow me when i take this patient to the burn ward?" There are similar programs in other EDs as well.
take home message: be open, flexible, and proactive
