Links of the Official LG G2 Stock ROM [Download]
Here is the list of all the official stock LG G2 Firmware / ROM. You can use these to re-flash the stock firmware back on to the device. I am not covering the flashing of the ROM here. Use the links to download the appropriate ROM for your region.
Also, do note that flashing the ROM might brick your device. Please proceed with caution in case you plan to do so. Also backup your data before flashing. If any links are not working or If you want me to add few more links, do leave a comment in the comments section below.