Note: I am not an attorney. The following are generalizations only based on my study of copyright law and are not meant to be construed as legal advice. If you have a question, consult a competent attorney specializing in copyrights and intellectual property law.
If the term of copyright has not expired and the author is not presumed dead, any work which is simply out of print and not available for public purchase is -still- protected.
You may not copy an out-of-print work just because you can no longer buy it.
The chances are reasonable that if you contact the copyright holder you may be granted permission in these circumstances (for one copy, probably), but don't assume this will be the case. And remember that you must secure permission first.
copyright 1996-2003, Martha Beth Lewis, Ph.D.