I was like you initially where I was searching for months for a DO physician to shadow and I was unable to find one. I got many "no's" or no responses (maybe not as much as you though). I did everything from cold calling, emailing, faxing, you name it etc. At least, in MY opinion, I found emailing and faxing does not work as well as cold calling but n=1. The ones that answered me are through cold calling and one from email (but this is an exception because it is a program with some random college. i wasnt a student of that college but i just asked anyways). I'm not sure why though, but after shadowing a couple of physicians, I can see that they might be too busy to answer emails or just overlook it by mistake.
If you do cold call, try the big hospitals around your area or call private practice offices. In private practice offices, you probably will be answered by an assistant and if you explain what you want and ask them to pass your number to the physician to give you a call back, maybe that can net you a shadowing position.
which state do you live in?