Stencil Street Art is a project by Katrin Winkel and Andreas Gohr. The site helps you find images of graffiti art created using stencils on Flickr. While you can select images based on tags, sadly, the option to search for images is missing.
Snip from the site:
It is a Flickr collection of photographies depicting streetart created using the stencil technique (sometimes called pochoirs). Most of the images were taken in Berlin, Germany but the phenomenon is seen and photographed around the world.