There was a 2 page thread very recently about how to go about finding doctors to shadow.
tl;dr The best way is to approach physicians you already know (family friends, your PCP). The next is to approach physicians you’ve met over the course of your clinical volunteering and ask them.
Ask physicians, not office staff–who are almost universally instructed to say no. Ask physicians in person, not by phone, not via email, because it’s much harder to say no to someone you’re talking to face-to-face.
UM has a shadowing program at the med school, but IIRC the waiting list to shadow is very long and it may take 6 to a year before your name rises to the top of the list. (UM has LOTS of pre-meds.)