i'm on fire tonight...
i wrote a post about this very issue a while back. if you can find it, i think i put some decent advice there (if i do say so myself). anyway, let's see if i can replicate it now...
first, are you doing anything in the health field right now? i mean, do you volunteer at a hospital or work at a clinic or something? if so, i'd start there. let people know you're interested in osteopathic medicine and that you want to shadow one. you may be surprised at what turns up. i found the first DO i talked to through a clerk i used to work with (in public health) who transferred to a hospital. i casually mentioned this stuff to her one day and lo and behold a while later i got a call from her telling me to call dr. such-and-such, DO. why? because SHE already talked to him on my behalf! go figure...
anyway, barring this, write a letter (print it at the library) and call to follow up. if one doc doesn't help you, move on. it's not because they hate you, but rather that they're busy. here's some advice, think carefully about what you're going to say before you call. i like one of the above poster's remarks; be clear about what you want. i straight up told the docs i talked to i couldn't get in without a letter and i couldn't get a letter unless i shadowed one of them. when you finally go there, think of it as an interview of sorts. remember, you're asking him/her to evaluate you and write a letter on your behalf. i was very lucky in that the doc i shadowed actually spent some time with me asking questions, answering questions, and getting to know me. of course, i had a resume ready for him when i got there, as well as a bunch of questions (all written down on a sheet of paper). being well prepared beforehand helped both of us a lot; it helped me get over my nervousness and him to not feel like he was wasting his time with a goofball.
anyway, if you can't find a DO that way, try the following. first, contact the DO school nearest to you. they may have a list of graduates who are willing to help pre-meds such as yourself. even if they don't, they can give you some good advice. they get this question all the time. second, consider contacting your state or local medical board. they can at least tell you where some DOs are in your area. you'd be surprised how many docs AREN'T in the phone book. third, if your state has an osteopathic medical society, contact them as well. they might be able to help.
don't be discouraged, you'll find someone if you keep on it. good luck.