Usually, very late in the process, the AOA or someone will send out a listing of the unfilled DO spots just before the AMA match or just after, I am not sure. One last chance to entice someone to cross over there....except for more DO (i.e.teaching) hospitals closing every year, try to make sure if you decide to go that route that the hospital is stable, and all you have to do is contact other residents at the hospital and ask if they can honestly recommend their hospital. My best friend was an obgyn resident at the last osteopathic hospital in Texas, and the hospital/residency closed down after 2 months of his internship! He desperately sought out something, anything anywhere, and finally had to re-locate to Indeanapolis (sp?), IN. He is fine now, but he would caution you to be very careful if not avoid that route altogether.
Hope this helps!