Some Walmarts carry 0W-20. Not all, I've found it to be about 50% of them in my area. A bit over $5/qt. Not much in stock though.

Possibly some 'outdoor sports' stores, too. I found some in "G.I. Joes" with other 4-wheel/snowmobile/etc maintenance things. About the same price as Walmart, and more in stock.

...because you'll see me passing everybody at 90 miles per hour going up mountains.