Hmm. I do not recall seeing that when I had my EX7. I guess they figured two hard drives would be enough.
Pat@ or support may be able to help, or I would just contact Clevo and ask them. Since they manufacture the system, they would definitely know and may be able to give you details on how to get one.
Let us know what you find out. I am sure there may be others who would also like to know.