Yeah Library of Congress is great for this type of thing... I had to use it a while back for something and I got great search results... The copyright can be an issue though - seems like the LOC has no idea about most of the stuff on there.
Currently I am looking for a nice old image to make a life size cut out of... not turning out to be an easy task.
"(re)view is a collection of retro images that each tell a unique story by capturing moments from the past. From humorous, kitschy images to heartwarming, emotional portraits, the collection contains timeless subject matter such as the innocence of childhood, friends, family, business and industry."
I have a quite similar problem and I don't know how to fix it, yet. I have a picture in RGB and when I change it into CMYK for printing, the colours are changing slightly. I need to get this fixed as...