You could find a prom dresses shop, and ask them help tailor for you. I know many shops do that :)
Well, it is made by a very exclusive brand, which is hard to get, because they only make haute couture. For that, you need an appointment in Paris, and a couple thousand dollars. However, it is possible to get a custom made dress, or a similar dress. For some pro dresses that are similar, look here. or on Etsy or Ebay.