Cruise the phone book. Make cold calls. Ask them if you can shadow. Make sure you express your interest in osteopathic medicine. Usually you will find lots that are receptive and a few that are enthusiastic.
If you have medical insurance change your primary doc to a DO and go in for a new patient intake appointment.
I found my DO after I was in a car accident. I let him know about my interests and he invited me to shadow him.
It never hurts to be aggressive in getting the things that you want.
Like the previous post already said, all you need to do is go to the physicians section of the yellow pages and look for the suffix D.O. You'll find that most D.O.'s (in my opinion so far) are very pro-education and want to help out any future D.O. in any way they can. I've had more positive experience shadowing D.O.'s than I have M.D.'s. Good luck.