If you haven't done so already, the Radio Kaikan in Akiba is a place that I recommend you stop by on your next visit.
Apart from K Books (doujin, eroge related goods) and spare Gundam parts, its worth making the trip just to check out the Kotobukiya store on the first and second floors.
This is the view from Akihabara station entrance - its the Denkigai or "electric town" entrance. The Radio Kaikan is the building that you see with the yellow sign.
And as with all the events they hold, there is usually a bunch of people gathering outside to take photos.
It seems that Kotobukiya have changed their strategy on what they sell on the first floor. Before it used to be full of figures but now its full of stuff that gajin are most familiar with - a lot of Totoro, Majo no Takkyubin, Final Fantasy etc.
If you walk in you will notice that their strategy is working as the place is usually full of gaijin.