You should be able to find a thermostat at a pet store. I got one at a reptile store, but they have them at petco too. In fact they were having a clearance on them recently ($9.98 ). Great deal, but I don't know if that is still going. Or you can get them online. LLL Reptile has a really good deal on one right now ($12.99)
http://lllreptile.com/v2/content/cat...att-thermostat