If you are in the States, some people have had luck with Lord & Taylor. Macy’s, or David’s bridal. Try finding a shell in a matching color if it is sleeveless or the neckline is too low. You can take a plain gown and embellish it yourself, if you are handy. Go to a trimming store and get a rhinestone belt or adding lace to the sleeves and hem will do wonders. Maybe go with a friend who has a good eye for these things helps. Or if you are not a sewer, maybe a tailor can help you fancy up the gown. Hatzlachah in your search.