I'm pretty sure you can only get the Relion strips at Walmart. I know the company that manufactures the Relion Confirm also sells the meter without the brand as the Arkray Glucocard and you can buy strips for that online, but I don't think they are compatible, so you would have to get a new meter.
I also have the Aviva, and I buy most of my strips on Amazon (sometimes on Ebay). For that meter, you pay about $50 for 50 strips at the store, but they're only $30 for 50 strips on Amazon, and cheaper than that if you can find a good deal on Ebay. I prefer Amazon because even though I might be paying a little more, I know the strips will arrive quickly and have a far away expiration date.