I just noticed, that oftenly the bonus tracks of some albums are missing, or can't be found anywhere. As an example, Avenged Sevenfold - St. James isn't included inside the Spotify's online-tracklist so I added mine MP3 to my list. I hope there would be a quick-request inside the program to request the songs which don't already exist in the online library of Spotify.
Hello and welcome to the community.
This idea has been suggested before, and is one of the more popular in the community. That idea can be found here: https://community.spotify.com/t5/Spotify-Ideas/Wish-box-for-missing-records/idi-p/173184
Please add your kudos and comments there!
And while you wait for that idea to be implemented, check out the link suggested by @Carina : https://community.spotify.com/t5/Music-Chat/Looking-for-an-artist-track-album-on-Spotify/m-p/934303