Yes, it's definitely going to be in the organic/natural foods section. Also look by the bulk foods. If your store carries rolled oats in the bulk section, it probably carries quinoa, too.
Our Walmart carries it, but it's not with rice and grains. It's in the health-food/specialty food aisle. At one of end of the aisle is gluten-free cereals, and at the other end of the aisle (where the quinoa) is a section of other grains, flours, and bread mixes. The brand Walmart sells is Bob's Red Mill.
I've seen it in other stores in the gourmet section, the health-food section, the diet section, even in the ethnic aisle, in bulk aisles, with the dry rice and beans.
Whenever you can't find something, ask for the store manager or ask at the service desk. They usually can tell you if they carry it and where it is (especially now as more stores are computerized, even the store manager may not be able to tell you whether they carry it, unless he looks it up on the store computers).
I buy it at Costco.
Most grocery stores have it now, though. You just have to look around for it. In the "health foods" section is a good place to start. Bulk stores are also a good place to buy it.
Our walmart sells it. It's in a small box and only has one facing, and is with the rices.. I agree though, ask a grocery manager and they should be able to help