Where do you get a set of (metric) thin open end wrenches

about to remove the rear calipers on my VW and there's a thin wrench (there's a term for this other than just simply called a thin wrench) that is just like a regular open end wrench but thin enough to squeeze into a tight space to hold the caliper bolt in place. A socket won't work because the bolt to be held is not accessible at the ends. (Note the picture shows a regular wrench but in my case, the last time I did it a regular wrench was too thick to fit in there. Tried Home Depot, NAPA, Sears, Advance Auto parts, nothing even close ... what are these wrenches called and where do I get them before this weekend when I planned to change out my pads and flush the lines? Any help is appreciated, thks