It's a shop called a-Too, a "media recycle shop" with a corner for used doujinshi.
It's on the second floor of Wanpaku Kozou videogame shop (were two days ago I bought Chrono Trigger) but until now I never went upstairs, so I was unaware of it .
The doujinshi selection is not very big, but is unorganized and mostly unlabeled. I spent a couple of hours checking the doujinshi one by one. This is the result.
Kurusugawa Ayaka by circle King Revolver. Now I'm only missing 4 from this author.
Geki!! Evangeline Ikka by circle BIG･BOSS. It was a rather prolific circle focused on Akamatsu Ken's works, but he doesn't release anything since 2005.
I don't follow Negima, but I like Chachamaru's strong resemblance with Serio.
And AVALON, a Fate/stay night fanbook released to commemorate the PS2 version of the game, with several pin-ups from different circles.