I have also been looking for this dress but by the looks of this article ( http://uk.eonline.com/news/504710/vampire-academy-s-costume-designer-ruth-myers-reveals-sketches-see-the-pics ) it was made specially for the movie. Saying that however, the shopping scene was filmed at my local shopping centre (Brent Cross, London) and I recognised the shop they were shopping in as 'John Lewis'. I have not found the exact dress, but as said above I don't expect to do so, I found this in John Lewis as a close-ish alternative.