google is your friend. Both adafruit and sparkfun have github repositories of fritzing parts for their products (some, perhaps many? of which aren't in core yet) both of those would be a good place to start. As well the google search "fritzing part device" (where device is replaced by the sensor you want) sometimes turns up a user created part that is available somewhere. Searching in the projects repository on the main Frtizing site will also sometimes find a project that contains an appropriate part that you can use. If all that fails you would be left with making your own part (which isn't all that easy, but assistance is generally available here).