A great collection of authentic old Halloween images can be found at the Vintage Ephemera blog. Wonderful inspiration for decorating and art. I especially like the Kellar ads–see below. (Kellar was the predecessor to Houdini; he performed large-scale magic acts around the turn of the century.)
Since the blog provides a database of all things vintage, I recommend searching the term “Halloween.” Below is a small collection of images I found, but there are tons more. Enjoy!