Cold outreach works far more often than people expect, mostly because so few students actually try it. Email physicians and professors directly, keep the message short and specific, and say exactly why their work interests you and precisely what you are asking for. Use every network you already have: your pre-health office, your school's alumni, and even your own doctors.
Do not be discouraged by silence. Send more emails than feels comfortable, because a low response rate is normal and a single yes is all you need. If in-person options are thin where you live, free virtual shadowing programs let you build real, documentable hours from anywhere.