I started using black flags more often a few photo-shoots ago, mainly to get that "out of black" look I like so much. So I was looking for a place to buy both the small A2 size cardboards ( to use with my soft boxes, or just hang next to the model, and a place to buy big industrial ( billboards) foam boards to really make a negative space.
I found two good places that are always in stock and have options:
The first, for the small cardboards is an art store next to Shida night market – bada art supply, located here (Google maps: 25.021969, 121.529312). you can get small ( A2 ) cardboards in any color, if you're looking to get a nice bounced off light , where except the yellow background, blond hair and gold necklace there was one light point at a yellow cardboard located just beneath the shot to get a totally yellow shot.
The second place is here – (Google maps: 25.048797,121.564803) phone: 02-27485397 called "open box" in English although you probably wouldn't find that name anywhere… they make signs, so they have very big foam boards , in different thickness. Don’t get there before 10:00 AM, they're still closed.
Why should you bother to get a huge foam board anyway? Because with a huge one you can make a "negative space" from two big foam boards sprayed in black paint, a black background and a black floor (cloth\another board) you can do these "out of black" shots.