Good luck. Many times, the sungalasses you see in movies are a special type, made only for the movie. The glasses in "The Matrix" were that way, athough some people found similar ones, but not exact replicas. In the case of a movie where the glasses are featured heavily (Men In Black) they usually will sell them to the public as consumer level eyewear.
My guess, check sunglasses hut or a similar place with a vast selection of glasses. You should be able to find something similar enough to make her happy.