The good news is: We add new content to Spotify every day, so if you can’t find something you’re looking for right now, it may appear (or reappear) soon, so please check back!
Does Spotify have a music request form for us to request adding a specific music track/album to Spotify? I would very appreciate if Spotify can add add this song, https://www.youtube.com/watch?v=8KTVQsfyCHM&list=PLz6e4iclyn3UQbhJgNtFpk5DmQ3ttxVtT&index=1, and all the songs from that album to the Spotify collection. It's the most beautiful song I have ever heard.
Artists, Publishers and other copyright holders can add their content to Spotify but, as we don't hold any copyright ourselves and only receive the license to add content, we can't really add tracks or other content on our own.
The request form will also stay offline, at least for the time being.
The content you don't see available on your end has a strict relation to licensing agreements.
As @AndresM has suggested though, you could contact the creator of the content through their artists' label on social media or their site and ask them what their thoughts on uploading to Spotify are!
Aside from that - the local files import is still a valid workaround. 🙂
Thanks & cheers!