Zappa's "rarities" often surface in posthumous box sets and archival releases:
(1996), and the multi-disc "Project/Object" sets for albums like (2006) and Lumpy Money www.zappa.com The "Beat the Boots!" Series In 1991, Zappa launched the Beat the Boots! Frank Zappa Discography Rar
Acquiring these rarities requires patience, knowledge, and a willingness to hunt. Here are the best places to look: Zappa's "rarities" often surface in posthumous box sets