Comment # 1 on bug 1180437 from Larry Finger

VboxAdditions.iso and the appropriate .extpak files have never been, nor will
they ever be, part of the openSUSE distributions. They are licensed with the
PUEL licence; however, the "open" part of openSUSE demands a GPLv2 or MIT
licence.

You need to download those files from Oracle. For the .iso, the GUI will offer
you the option of downloading the file.