White Cat-Eye Sunglasses - Margot Robbie - Barbie
Margot Robbie also wears pink Chanel glasses in the same film. Robbie is a brand ambassador for the brand so she wears Chanel shades in the film.
Similar cat-eye frames are the Chanel 5481H ($520 on the Chanel website).
You can find similar white cat-eye sunglasses on Amazon.
Ray-Ban also offers a very nice white cat-eye model, the Ray-Ban RB2299 Lady Burbank, available on Amazon for $189.
Prada offers the bi-color Cat-Eye frame with white front and black arms, see it on Designer Optics.