I detoured through the oil isle today while grocery shopping and noticed they had SynPower 0w20 in quarts for $6.57. They only had two but i was surprised to see a second brand in 0w20 at Wal-Mart. It was SL/SM rated.
My local Walmart Valvoline Synpower 0W20 for many months now. It is also available at Pep Boys. The one 0W20 that can not be found at local stores is PP.
I wouldn't be surprised if we start seeing more 0w oils stocked in stores in the coming years as more car manufacturer's start recommending it. Though most that recommend it, usually state that 5w can be used in its place if 0w isn't available