Missing Materials Library

I have a master file series that I have been using for years for Iray renderings. I imported another file with Iray materials into the main file. I got messages at autosaves about four missing materials. Rhino command-line showed successful save. Closed file, re-opened, entire material scene library blank. All materials render white.

edit: opened up two week old backup 3dm file, library also blank, obviously stored outside of the file.

Where are the materials saved so I can restore?