They are indeed hard to find outside of Best Buy... although when I was shopping around, I did find some folks selling on eBay, and one other seller had them but they were a little more expensive... just need to be careful not to get the Z-Wave version.
Here's the link that takes you to the Best Buy page where they sell the Zigbee model that we need: http://www.bestbuy.com/site/promo/xfinity-and-kwikset-134972
Right now, they only have Venetian Bronze available... but when I checked a few days ago, they had all three... so they're probably workign to re-stock.