What country are you in? The device selection does vary somewhat.
As far as doing a search and not finding anything, did you check the community device class features FAQ? There are links in that thread to threads about lots of different devices, including temperature sensors.
Bulbs, switches and sensors, oh my....what to buy (device class features FAQ)
Also, how accurate do you need to sensor to be? Most of the inexpensive ones that work with smartthings for home automation Are really intended for HVAC controls. So within about 2°F is usually good enough if it means the sensor can be less expensive. But that might not be sensitive enough for some users.