You can get Kut Ku ears on any Yian Kut Ku hunting quest. Either capture him, or break his ears, and you will get an ear in the rewards. This can be difficult as he usually dies before his ears can be broken. I've found the best way to get those is in the download quest The Mysterious Kut-Ku, where you have to kill at least two mini Kut-Ku. Since they're much smaller, your hits usually break their ears no matter where you try to hit them.