Good news guys!
Found a store that has some 3DS and 3DS XL consoles with firmware version 4.5 and lower! It's a store in europe but they deliver worldwide!
http://www.dynamodz.com/videogames/nintendo-ds/nintendo-3ds.html?cat=298&___store=english&___from_store=english...
@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