I know for a fact, cause I have bought mine there, that Nordstrom carries them. Ohh and http://www.solsticestores.com
i know the manchester harvey nics has sunnies too. i should think optical stores would have dior sunnies too. or eBay. i just got a pair of eBay seller - eyewearer - very prompt shipping and it's authentic. and they do have a 7-day refund policy.
I bought mine off neimanmarcus.com. I've also seen them at Nordstrom.
Bluefly.com has them.
bloomingdales also has them. Small high-end sunglass botiques usually carry them as well.