Well, technically speaking, library music was never commercially available
I was just gonna say this but Stack already did. For reel to reel library, I know the Network catalog was available on reel to reel through them directly.
However, all of the KPM, Selected Sound, Sonoton, Bruton, etc was also on reel to reel here in the US through Southern Music. Roy Cohen (the guy that controlled Southern in America) was the middle man for all of that here. Any time a TV show or film would licence something from the non-US libraries like KPM, etc, it would always be listed as Southern Music over here. Of course, Southern/Peer's direct in house material was available on reel to reel as well.
You also had your reel to reel only libraries that never pressed vinyl. All reels for any were available on both 7 1/2 ips speed and 15 ips speed.
Finding vintage library reels for sale 2nd hand are a mega rare find.