Look for the copyright statement. If the work is copyrighted to the publisher, write to them. If it is copyrighted to the author, write to the author, care of the publisher. If the author is dead, the publisher should know the literary heirs. If the publisher is now untraceable, try to write directly to the author or his/her heirs. There are some web sites which help for literary figures, especially WATCH: Writers, Artists, and Their Copyright Holders (www.watch-file.com/). If you can demonstrate you have made best efforts but failed to trace the copyright holder, then a note to that effect and a promise to act upon the wishes of the copyright holders, should they emerge, should be enough to defuse any potential legal situation, but in cases of doubt you do need to seek legal advice before making what is, after all, a prima facie infringement.
Note that you cannot write to a copyright-holder to the effect, 'If I do not hear from you, I will presume that you give permission'. Consent must be explicit.