I would guess that a lot of this music wound up on compilations by now-defunct labels like Pacific Jazz.
There is a UK reissue house called Proper that is taking advantage of the disparities between US and UK intellectual property law to pronounce lots of 50+ year old music as "public domain" and to sell it at a very low price (US$14.99-19.99 for a 4 disc set).
They have, for example, a cheap box set of more than 120 recordings by Artie Shaw's orchestra.
Do you have any idea of what some of the frequently used titles were?