Pixiv Zingaro is an exhibition space on the second floor of the Nakano Broadway shopping complex. They usually have artwork exhibitions there, and when I went they had a Super Sonico the Animation one. The nearest train station is Nakano station. Inside Nakano Broadway there's maps on each floor, and on the second floor ones Pixiv Zingaro will be named in English.
Believe it or not, it's actually quite easy to miss this place because there's loads of interesting shops all around.
They had a lot of Super Sonico the Animation shots up on the walls.
There were also some of these sketches.
And a display case with some goods.
When I was there they actually played the YuruYuri OP from one of the Super Sonico CDs.
This location was visited on 2014/04/14.
Pixiv Zingaro official website