The truth is...there is no real set COMLEX score for many programs. DO residencies want to know that you are academically sound and that you have people skills. Getting the residency, like I was told, is much like getting into DO school. They look at the whole person, the whole application, the whole package. Board scores are just a part of that big package. In fact, to answer your other question, you can narrow down the residency programs by choosing hospitals based on other factors such as geographic area, for example. That will at least give you an idea or a direction where to start your search. Then, try to rotate through them for a couple weeks. If that's not possible, try to visit them and have lunch with with the program director. I'd say with borderline board scores (even passing) and a good attitude and a great work ethic, you'll increase your chances dramatically. I hope this helps.
Atlas