I found this Bisou Bisou long sleeve dress available at JC Penney. With its round neckline, long length sleeves, and high slit, this version definitely resembles Kate's, although unfortunately only comes in black.
Strangely it seems to be unavailable on the website right now. Maybe its a black Friday thing because I still saw it in-store today, but you can check out the line of Bisou Bisou dresses here.
|Bisou Bisou at JC Penny - long sleeve dress.|