It's a great book. The one I have (Canadian) has an index by description & by part # & illustrations. There was one on eBay not long ago but was big $.
The 64-72 edition is online at 65gs.com: http://65gs.com/wp-content/uploads/2017/07/1964-72-Buick-Master-Parts-Catalog.pdf
Here's a 1940-1970 for sale, just posted today: https://v8buick.com/index.php?threads/master-chassis-parts-catalog.377218/