I have always liked this song that was used for the trailer to Sonic Advance 2 in the Sonic Mega Collection. But when I went to look for downloads of that specific song, I could not find any results that was the original song. It makes me wonder do high quality rips exist of any of the beta music to that game? I figured this forum was the right place to ask that question since I could not find results elsewhere. Most websites claim it was the beta music for Leaf Forest Zone, but the Sonic Retro wiki page claims "During the Sonic Advance 2 preview in Sonic Mega Collection there is a track that is nowhere to be found in the final game. There is much debate on whether or not this was intended to be used for Leaf Forest." If anyone here has additional information about this song or any other scrapped music from the game, that would be awesome.
Seeing as we have no Advance 2 protos and it is only speculation that the music is from an Advance 2 proto, someone coming out with more "unused music" from the game seems like it has a small chance of happening. As for your other question, there used to be downloads for this specific piece of music everywhere in the community back in the day when hosting music was the norm for the various community sites. So maybe someone can give that to you. It's probably best that someone makes a new rip of it though.
I remember a forum thread here was made a long time ago about a build that was found, but it had hardly or no differences compared to the version of the game that released. For whatever reason, I can't find the thread with the search feature on this forum. If I could get the highest possible quality rip of the song, that would be wonderful.
That would probably have been @Orengefox if I remember correctly. That one had byte differences but that was it if I remember correctly.
I had actually done a rip of this theme for myself, last year, where in I found the .SFD video file, demuxed it, converted the .ADX audio stream, and then trimmed out the song, resulting in the best quality you can get for this song, unless a ROM is found with the song, and a GSF rip is made. A download link to the rip can be found here. The notes text file explains what each file is: https://drive.google.com/file/d/1oX2138Uv7Wt0PkoiKGnHahIkfWbRVCe5/view?usp=sharing