Rather than poring through magazines (I don't really have any) to find resources for this level of V/V, I really like Flickr's Interestingness Calendar. On this page, Flickr features 6 photos per day, uploaded by users that are interesting in terms of content, color, and composition. You would want to look ahead of time and bookmark the URLs of images you find appropriate for therapy.
I have found it helpful to combine V/V activities with Story Grammar Marker- after the picture is described in detail, it can serve as a story starter!
I need to emphasize that the Interestingness Calendar is something you can use to bookmark and/or save images you can use with students, but you should not go there and click around during a session. Like all photography, some of the images are, well... provocative. You can click through to an image and bookmark it in your browser or diigo. You can save SOME Flickr images (some users do not allow you to download their pictures, understandably by selecting Actions above the full-size image, then View all Sizes, then click the size to download. If this doesn't work, you can always bookmark and display the image on your laptop, iPad or iPod touch during a session.