I was looking for some vintage stock photos today and came across a group on Flickr with a focus on collage imagery. You have to join the group to view/download the images. Within the group you can view the vintage tagged photos. As always, make sure you read the copyrights for the images as each photographer has their own terms of use. Most all the images are free for personal and commercial use; however, you cannot repost the images on your website for download or sale.

Another good resource is the How to find images on the internet post.