Great question! Walter White’s iconic sunglasses are of the Wayfarer style. This is a rounded rectangular, wraparound model.
If you are shopping for some, search for ‘Terminator style’, or ‘Wayfarer’/’Rounded rectangular’ shape.
If you are in a hurry, here are a couple of cheap options!: this $7 pair from Amazon – or these are cool too for $8.25.
Walters sunglasses are by the brand Smith Optics and the model is the Turntable. Sadly they are discontinued.