The first step to finding an appropriately styled ceiling mount for an antique fixture is knowing that it's called a canopy.
I have purchased an antique light that I would like to use as a hanging fixture. Currently, it has an electrical cord on the top with a plug (that is how it was previously used). I need to know what the piece/plate is called that covers the hole in the ceiling that the electrical cord goes through so I can buy something of similar age and style.
What you would call the cover plate on the ceiling is a "canopy". Take a look at www.antiquelampsupply.com . They have a lot of canopies from which to choose. You should be able to find one that matches the look and finish of your chandelier.