Update - the 2010 article on Nakano Broadway lives here.
Been living in Tokyo for many years and only recently learnt that Nakano Broadway was another Otaku heaven. Heard much about the place so thought I would go along to see what the fuss was all about.
This is the shopping arcade leading up to the huge Nakano Broadway shopping mall - its just outside Nakano stations North exit (JR Soubu line). Unless you have two red hot steel rods stuck in your eyes, you cant miss it.
Nakano Broadway has 4 floors where the second and third are filled with Audio, darts, adult dvd, army wear, idol posters, figurines and a ton of other otaku gear. Its more likely that you'll find some of that rare stuff that you're looking for here rather than Akihabara.