This time, we have a commercial livery, the only Boeing 777-300ER Alitalia had with its classic colors. 
The registration of this aircraft was EI-WLA

Unfortunately the mod isn't available on gta5-mods, but you can find it here:
https://libertycity.net/files/gta-5/199662-boeing-777-300er-add-on-replace.html

Tutorial: To use it you can either replace one of the liveries already present
or add it by changing the number of the .dds file depending of how many liveries you already have.
Place the livery in the following directory: 777300er>dlc.rpf>x64>levels>gta5>vehicles>mq1vehicles.rpf>773er.ytd

Enjoy!