There’s a certain period of time that elapses between the need of downloading virtual box and of course it’s additions (VBoxGuestAdditions).
AND each time it seems that I loose that bookmark of the beautiful download site of “sun” products.
So… without any farther delays it is HERE. ( http://dlc-cdn.sun.com/virtualbox/ )
At the top you will find all the versions by their number.
Click the desire version and you will find the addition inside.