Due to the release of Collection of Mana, I can't host any music files here for Secret of Mana. Rather, I can provide you with links to official services and other sites.
Fortunately, Square Enix has made it easy for us to listen to the soundtrack for Final Fantasy Adventure. It's available on every popular music streaming platform.
Square Enix hasn't officially uploaded Final Fantasy Adventures's soundtrack to any platforms. I need to direct you to fan-uploaded OSTs on YouTube.
The best place to listen to Final Fantasy Adventure fan music is at OverClock ReMix. They offer hundreds of songs! They have also uploaded their music to YouTube.
Here are album covers for the soundtrack. Some official ones and some custom made ones.
Square Enix hasn't officially uploaded Sword of Mana's soundtrack to any platforms. Sword of Mana is one of those spin-off games that they seem to want to forget ever existed. Fortunately, people have uploaded its soundtrack to YouTube.
Here are some album covers for the soundtrack. The first one is the official cover. The other I made from the title screen.
The fan base has gone a long way with emulation. In the early 2000s, they came up with 'extracted game music' (a.k.a. chiptunes). They extracted the programming of the music from every classic video game and built digital soundtracks with them. With special music players, you can play these music files as if they were MP3s. And they're far better quality than MP3 because it's the actual programming of the song that you're listening to! In this realm, Game Boy Classic music is under the 'GBS' file format and Game Boy Advance music is under the 'GSF' file format. Music players that support GBS and GSF can be found on any device: Windows, Android, iOS, Mac, and Linux.
My favorite feature about this music is how small it is. Final Fantasy Adventure's GBS soundtrack is around 20 KB while an MP3 soundtrack is around 100 MB! Sword of Mana's GSF soundtrack is around double the size. So you could quite literally have hundreds of classic gaming soundtracks on your iPhone or Android phone, and barely make a dent in your phone's storage.
If you want to learn more, read my tutorial for Extracted Game Music. My tutorial also provides links where you can download Game Boy Clasic GBS and Game Boy Advance GSF music. Extracted game music can be converted to MP3, too. My tutorial provides directions on that process.
MIDI music is a relic from the early days of the Internet when it was the only music we could download with our slow dial-up connections. It's fan music because MIDI files are made by people playing the songs on electric keyboards. The #1 website for video game MIDI music still exists today: VGMusic.com. There you can download Final Fantasy Adventure's entire soundtrack in MIDI format.