"Missing or unavailable music is almost always a decision by the artist/label to withhold the content from Spotify. Sometimes it's temporarily unavailable while they sort out legal issues or correct metadata, in which case it'll be back up as soon as they resubmit it to Spotify. It might be a good idea to contact the label directly and ask why the music isn't on Spotify!" - Jacob
Basically, it looks like you need to contact the managing label, asking them to register/upload their music to Spotify's library.