I didn't realize you can rent a SIM card in Japan. Thanks for the tip!
Originally Posted by
railroadtycoon
You want to check out Nakano Broadway (Nakano Station, North Exit, where the real Otaku go

)
Looks like Mandarake has a big shop in Akihabara as well:
http://www.mandarake.co.jp/en/shop/cmp.html
But I will definitely try to visit Nakano. Thanks for the tip