It looks like Will Smith is wearing SALT Optics Wyatt sunglasses in Men in Black 3. Although we're not 100% sure yet and we can't find any reference on this anywhere, it really seems that Will Smith changed his Ray-Ban's for these SALT Optics frames. The Wyatt model seem to be the same as the glasses in the film, and on one promotional event, Will Smith held up sunglasses on which we spotted the SALT logo on the inside of the temple.

The $400 sunglasses can be found on the SALT webshop, Amazon.com or eBay.