“Does not exist” is a flexible term in Fritzing 
, they are not in the standard library shipped with Fritzing but many parts are not. A google search for “fritzing part Adafruit Ultimate GPS Breakout version 3,” and “fritzing part DS18B20” turn both of them up in the Adafruit Fritzing library on github:
https://github.com/adafruit/Fritzing-Library/blob/master/parts/Adafruit%20Ultimate%20GPS%20v3.fzpz
https://github.com/adafruit/Fritzing-Library/blob/master/parts/DS18B20.fzpz
You can either load the entire library in to Fritzing (instructions on Adafruit’s site somewhere as I recall) or just download the 2 fzpz files and then load them in to fritzing via file->open->filename.fzpz which will place them in the mine parts bin ready for use. Other times you may find parts (of varying quality) from other people. If you try and use such a part and it doesn’t work, post a pointer to it here and probably one of us will take a look at it for you. If you can’t find one online post a pointer to the data sheet for the part here and someone may choose to make a new part. Many parts are posted here in the forums and while google will find them as well, using the forum search can be useful as well.
Peter