Air Scroll In the Air Temple (Chapter 6), head west and north after leaving the temple. When you get there you will have to play "The 4 Nations Force" game with the spirit of Gyatso. You will get an Airbending Scroll whether you win or lose. Use it to get a tornado-like attack for Aang.
Earth Scroll In the Air Temple (Chapter 6), go to the south and find the Earthbender. Talk to him and win the challenge. Then, use the Scroll. You will get a move that is similar to Haru's Boulder-Kickin'.
Water Scroll In the 4-Paws Island (Chapter 5), go through the middle of the island and turn upside. You will encounter a monster. After defeating it, it will hide. Follow it and search for the yellow chest. Enter two key items and use the Scroll. You will get a water bending power for Katara.