Mike -
Summit Glass, Viking Glass, John J. Biondich (Plum Glass), Peletier Glass Company, Allegheny Opalescent Glass Company, Blenko Glass, Brooke Glass Co., Loris Drug Store, Jeanette Shade & Novelty Co., Pairpoint Glass Co., Phil Rosso, and Premier Images, Inc are the documented companies that bought some of Westmoreland moulds when they closed.
There is a list of the moulds in the front of Collector's Encyclopedia of Milk Glass by Bill & Betty Newbound. The also have list of where Imperial moulds ended up.