Solution
When creating a volume license installer (VLI) from NI Volume License Manager, the installer wizard will ask the user to point to the source directory:
Although this field typically points to some sort of physical media present in the system, it is not mandatory. In order to create a VLI without physical installation media, the user must instead point this field to the location on disk where the installation files reside.
Most National Instruments software is available to download online. These downloads are
.zip files that contain the installation files for the software. Once the contents of the
.zip files are extracted, the VLI can use this directory as the source directory. The default directory for the unzipped installation files is
C:\National Instruments Downloads (Windows).