Hmm, I guess you can't install a virtual package through dpkg. You should be able to get this through your package manager. I'm guessing you don't have the right repositories enabled, which is why apt wasn't able to find the package. Or you need to refresh your repos.

Code:
sudo apt-get update
Search for the package name to see what it's called exactly.
Code:
sudo apt-cache search linux-restricted-modules
If it's not found, post your sources.list. You can open it up as so.
Code:
gedit /etc/apt/sources.list