I tried a couple of times to find certain audiobooks, but seldomly had luck. There just does not seem to be a place that sells digital versions of audiobooks, similar to how bandcamp sells music.
And even putting on my eye patch and throwing out my fishing net I was not able to find a place to get them.
I do not want to use a subscription service, especially if it’s part of amazon.
Therefore it seems buying a CD and ripping it is the only option left.
Spotify has surprisingly many audiobooks (at least in Germany).
In case you want to play them someplace else, you could download them with zotify.