It's broken

My thermastat cover broke off this morning.  Anybody know how I would replace it?  Hardware store?  Or since it's plastic, am I just plain out of luck?  I can always turn it on and off with pliers (like I do my crockpot that also broke) but it's such a pain using a tool. Problem is, this room gets cold fast and because it's kind of small, it warms up fast and gets too warm with the heat on. Which is why it probably broke. I'm always messing with it. Suggestions?