Unfortunately, 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. While it might be a good idea to contact the label directly and ask why the music isn't on Spotify, you can also use Twitter and Facebook to ask the artists themselves.
You might also be interested in supporting this idea, which suggests a simpler method for requesting albums missing from Spotify.
Let me know if you have any other questions.
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