Only download ROMs for games you physically own. This is the "backup" defense. If you own Chrono Trigger on DS, downloading a digital copy for preservation is legally defensible in most jurisdictions.
If you are searching for specific "pieces" or sets, try these terms in the Archive search bar: "Nintendo DS No-Intro" "NDS ROM set" "Ghostlight NDS" (for European releases) "Nintendo DS Decrypted" How to download files - Internet Archive Help Center nintendo ds roms archiveorg