Looks like Amazon is one, if you purchase by 4/21.
"Buy a Qualifying Panasonic VIERA HDTV and Get Two Free Pairs of Active Shutter 3D Glasses
To take advantage of this offer, simply add a qualifying Panasonic VIERA HDTV and two pairs of the Panasonic 3D glasses from the list below to your Shopping Cart. You must change the quantity of the glasses to two in your Shopping Cart. The discount for the glasses will automatically be deducted at checkout. Qualifying products must be shipped from and sold by Amazon.com; does not include purchases from other sellers on the Amazon.com website."