Got mine at walmart also, in the hardware/housing section near all the fixtures. There should be an actual section that is just for temp/humidity guages. Our walmart had a pretty large selection but I chose the acurite due to recomendations on here and comparing them to the others at walmart!
Not home and garden, look in hardware. They keep them next to the rheostats and dimmers at my local walmart. Or just go to walmart.com and order them...or send it to your store. Either way, they're out there.