Edit: Sorry. This is wrong. This is for 16oz
They originally released it on Amazon as a way to test the market. Then some stated started seeing it pop up in Wal-Mart. Just recently they did a huge re-release of the product, but it really only happened for the midwest and east of the Mississippi River. You can check out their site to see where you can get Surge, but you'll notice that there is nothing listed in Colorado.
Right now your best bet is still Amazon.
They are only sold on amazon.com officially. So you would have to pay amazon price + a markup if you found a local place reselling them or another online shop.
Just buy on amazon and they deliver to your door. http://www.amazon.com/SURGE-12-16-FL-Cans/dp/B00OK0I4AO