"The problem is Apple doesn't provide a Boot Camp driver set for the Retina MacBook Pro yet. I had to use the Broadcom wireless driver from my SNB MacBook Pro to get WiFi working under Windows."
Okay, after a bit more of searching online, found the driver, installed it and it works. Here's the link for anyone else who might need: http://www.wireless-driver.com/broadcom-wireless-driver-utility-winxp-vista-win7-ver51001968/
I don't have a Retina Macbook Pro but what I would do in your case: Download trial of Aida64. It will help to detect network chip, then go to manufacturer's site and download drivers (probably that would be Windows 7 ones) for that chip.