Hey, welcome to the Spotify Community! Don't worry, we'll be able to assist you whenever you need it!
The original song is not on Spotify because the rights owners haven't either sold it in digital stores or uploaded it to Spotify specifically. It's not Spotify's fault if the track can't be found. Try asking the rights owner (record label, movie distribution company) whether or not the track has to be published.
Hope I've helped; welcome again, and enjoy Spotify! 🙂