1michael1,
If I am understanding what you are asking, which is “how do you obtain the installer package, while in runlevel 3” The simplest way to do this, would be to download the package, while in run level 5, say to your desktop. After the package is downloaded, Use Ctrl+Alt+F1. This will bring you to your terminal.
After in terminal, and once you have logged in as root, you would than issue the following commands:
init 3
cd /home/username/Desktop *Replace "username" with your username.
sh PackageName.run
Than once the installer has run, and completed, issue the following command:
init 5
This should accomplish what you have been trying to do.