SoShow is awesome, they have lots of anime/manga shops, I love that place!! haha
Besides that, you can try going to Gulou Dong DaJie, which is close to Drum Tower. They have a lot of anime/manga shops, too, and some shops which sell especially Doraemon products lol. It's one of my fav streets in Beijing.
I want to know about the cons in June, too!