They stock the bulbs from the first three links in the Walmart near me, although it is a super walmart, so I'm not sure if that makes a difference. They are not in the pet section, but back with all the other light bulbs. They come in packs of two. For anyone looking to buy these, I would suggest seeing if there is a super walmart within reasonable traveling distance from your house, and see if they'd have them, too. The color temperature of the ones I bought there in the store was 6500K, and the 15 watt bulb was 800 lumens.
I have to warn everyone, though, that the bulbs are short and fat. Most CF screw in bulbs I have seen are more narrow than these. It barely fits in the fixture for my 2 gallon hex tank, and the plastic base is actually touching the reflector. I am not sure if the higher watt bulbs are even larger or not, but it would be something worth thinking about before ordering a case of them!