I got my covers from here:
http://www.web-emulation.com/jaquettes-jeux-nintendo-en-0-9.php
I just cropped them. They're much nicer than the ones that showed up from google.
@Xdqwerty, Osu! Tatakae! Ouendan! is the Japanese version of the game, different settings/characters/songs but otherwise identical mechanics. I played that before I knew about Elite Beat Agents lol. Both fantastic games https://en.wikipedia.org/wiki/Osu!_Tatakae!_Ouendan