Launchpad-getkeys is a script that imports these missing keys automatically.
When adding PPAs to Ubuntu via apt-add-repository the PPA and its key will be imported.
These GPG keys are a way to verify the packages in that PPA.
Ubuntu Forums user (blackgr) created a script called launchpad-getkeys that will import all missing keys automatically.
sudo apt-add-repository ppa:nilarimogard/webupd8
sudo apt-get update
sudo apt-get install launchpad-getkeys
Launchpad-getkeys is now installed.
