The latest firmware for LG US730 is “US73010a” revision “US73010a_19”.
Just noticed that someone is requesting the official firmware for lg us730.
Here you are the direct download link for lg us730 firmware “US73010a”
also you can try to download the firmare from this link.
The firmware comes with a .cab extension. You need to convert it to a .kdz file so that you can flash the firmware on your LG US730 cell phone. Just google “How to convert LG firmware .cab to .kdz”, You will find the tools & utilities to convert the firmware file format.