It's often not possible to obtain the WWAN antenna separately. People have asked previously in these forums. Parts-People is a reliable source of genuine Dell parts. They sell WLAN antennas separately, but not WWAN. They do sell complete displays that include WWAN antenna. It can be challenging to install a WWAN into a display that didn't originally have it. Many parts of the display assembly are glued, so the risk of damaging the display is high.
Does anyone know if is possible to buy the WWAN antennas for the dell latitude 7300? My motherboard has the WWAN card slot, and the sim card slot, but don't have the WWAN antennas, and I really need those, if anyone have the info I will be so grateful   
Latitude 7300 wwan antennas