Free Music Archive has been one of my go-to places to find free music to use video projects. Unfortunately, the end is near for the Free Music Archive. Earlier this month the hosts of the FMA announced that it would be shutting down at the end of the month. That's just ten days from now!
Fortunately, all of the FMA's collections will be posted on Archive.org. You'll be able to access the music there. However, Archive.org doesn't have nearly enough filters to make it suitable for classroom use. What you could do is go into the FMA archive yourself and download some music that you then put into a Google Drive, OneNote, or Dropbox folder for your students to access.
And if you're looking for some alternatives to the Free Music Archive, you can try Dig CC Mixter, The National Jukebox, or Musopen. My video overview of Dig CC Mixter is embedded below.