Hey Alecrim, welcome to the Spotify Community!
Missing or unavailable music is almost always a decision by the artist or record label to withhold the content from Spotify. Sometimes it's temporarily unavailable while they sort out legal issues or correct metadata, in which case the music be available as soon as they resubmit it to Spotify. While you may choose to contact the artist or label directly and ask why the music isn't on Spotify, you can also fill out this form to let the Spotify staff know of your interest. You might also be interested in supporting this idea, which suggests a simpler method for requesting albums missing from Spotify.
Hope this helps!
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