During Monkey Madness, one of these is obtained from the Monkey Child. He asks for 20 bananas in exchange, but you only have to give him 5, because he can't count. To get another monkey talisman after that, talk to him again. First you will tell him that you lost it and he will start to cry. You can either log out of the game, or wait for around a minute (watch out for The Monkey's Aunt or use a greegree) and then he will cheer up, allowing you to take another one.