The two we use all the time are (1) _The Official Museum Directory_
put out by the American Association of Museums - we have an old
copy with an 800# listed for ordering: 1-800-323-6772. Some
members of this list are AAM people who will have more recent
info.. (2) _Museums of the World_ published by K.G. Saur Verlag
KG, Munchen (printed in Germany but done in English.)