I find wonderfully hideous 80's cassette tape racks and boxes at my local thrift store all the time. Guess what is the exact same size as a cassette case ? ?
This one holds 30 carts! More often than not I get open racks, so this Famicom briefcase was a lucky find. One day I'll repaint the racks and mount them on the wall or something to store all of my games. If you can find some, they fit Sega Genesis carts too.