I honestly don't think that this is a necessary requirement in order to get into medical school.
For example, if you've had undergraduate training in a hospital as part of your degree requirements, if you've worked after school in a hospital setting, and if you have some general volunteer experience, I don't think it matters whether you have any physician shadowing experience. It COULD help get you a letter of recommendation (maybe...although shadowing experiences last like a day, so is that REALLY enough time for someone to know you well enough to write you a LOR? Nope.)
You really have to know people in order to get this type of experience. Cold-calling is ridiculous...loan officers cold-call people about their mortgages, and likewise, this is a horrible way at trying to get shadowing experience. So therefore, I'm leaving this out of the application process. Shadowing is all about observing...that's all you'd do is observe. I know how a hospital generally operates, and the overall ambiance has sunk in enough to tell me that YES, I'm ready to become a physician. Bang...that's it.
If during an interview, an adcom were to ask me, "Why didn't you get any shadowing experience?", I'm going to respond with, "I'm a doctor, not a loan officer!" (Yes, I swear to god I'll say that if I'm asked LOL).