Just discovered that you can download single images of the Allen Brain Atlas as SVG-files. This tutorial explains how to download the vector files. The simplest way is to use this URL in your browser

http://api.brain-map.org/api/v2/svg_download/plane_id?groups=28

Where plane_id is the id of the plane you want to download, e.g.

http://api.brain-map.org/api/v2/svg_download/100960084?groups=28

Very cool, that they share all the data in an open source vector format.