The first time I posted this to r/MyNintendo it was glided! https://www.reddit.com/r/MyNintendo/comments/69x68j/every_single_my_nintendo_wallpaper_to_date_free/

This site includes the European and Japan-exclusive wallpapers. It's super easy to scroll through and you can even filter by the size! https://mariomasta64.me/my.nintendo.com/