The Avant Garde Project has a large collection of free music that you can download, including digitized LPs of long out-of-print electronic music works:
The Avant Garde Project is a series of recordings of 20th-century classical-experimental-electroacoustic music digitized from LPs whose music has in most cases never been released on CD, and so is effectively inaccessible [...]

 

 A Fluttering of Wings [14:47m]: Play Now | Play in Popup | Download