I bought the book online via Yesasia. And I'm sure you can find sheet music there with Niji in it as well, if you're searching for a hardcopy. :) Otherwise, I referred someone else earlier to where you can find Niji scores so I'll just c&p: winkychan has it here (http://winkychan.livejournal.com/15429.html) along with a huge collection of more Arashi songs (basically a treasure trove for pianists). And yuri_senritsu has a great transcription of the concert version here (http://yuri-senritsu.livejournal.com/30233.html). :D