problems installing Virtualbox on Trisquel 7.0

Hi,
I'm using Trisquel 7.0 (Libreboot X200, 4GB RAM and 160GB HDD). I'm doing
an online course which requires Vagrant and VirtualBox (unfortunately not
free software). I tried following the instructions at:
https://trisquel.info/en/wiki/installing-virtualbox

These are:
--------
sudo apt-get update
sudo apt-get remove virtualbox virtualbox-ose --purge
sudo apt-get install linux-headers-`uname -r`
sudo apt-get install virtualbox-ose
sudo aptitude install linux-generic
sudo adduser $USER vboxusers
--------

But I had the following problems:

~$ sudo apt-get update

Hit http://nl.archive.trisquel.info belenos InRelease
Hit http://nl.archive.trisquel.info belenos-security InRelease
Hit http://nl.archive.trisquel.info belenos-updates InRelease
Hit http://nl.archive.trisquel.info belenos/main Sources
Hit http://nl.archive.trisquel.info belenos/main amd64 Packages
Hit http://nl.archive.trisquel.info belenos/main i386 Packages
Hit http://nl.archive.trisquel.info belenos/main Translation-en_GB
Hit http://nl.archive.trisquel.info belenos/main Translation-en
Hit http://nl.archive.trisquel.info belenos-security/main Sources
Hit http://nl.archive.trisquel.info belenos-security/main amd64 Packages
Hit http://nl.archive.trisquel.info belenos-security/main i386 Packages
Hit http://nl.archive.trisquel.info belenos-updates/main Sources
Hit http://nl.archive.trisquel.info belenos-updates/main amd64 Packages
Hit http://nl.archive.trisquel.info belenos-updates/main i386 Packages
Ign http://nl.archive.trisquel.info belenos-security/main Translation-en_GB
Ign http://nl.archive.trisquel.info belenos-security/main Translation-en
Ign http://nl.archive.trisquel.info belenos-updates/main Translation-en_GB
Ign http://nl.archive.trisquel.info belenos-updates/main Translation-en
Reading package lists... Done

~$ sudo apt-get remove virtualbox virtualbox-ose --purge
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package 'virtualbox' is not installed, so not removed
E: Unable to locate package virtualbox-ose

~$ sudo apt-get install linux-headers-`uname -r`
Reading package lists... Done
Building dependency tree
Reading state information... Done
linux-headers-3.13.0-57-lowlatency is already the newest version.
The following packages were automatically installed and are no longer
required:
apt-clone archdetect-deb cifs-utils dpkg-repack gir1.2-timezonemap-1.0
gir1.2-xkl-1.0 libconfig9 libdebian-installer4 libgtkmm-2.4-1c2a
libtimezonemap1 python3-icu python3-pam sbsigntool
Use 'apt-get autoremove' to remove them.
0 to upgrade, 0 to newly install, 0 to remove and 280 not to upgrade.

~$ sudo apt-get install virtualbox-ose
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package virtualbox-ose

I also tried the debian wiki for virtualbox:

~$ apt-get install linux-headers-$(uname -r|sed 's,[^-]*-[^-]*-,,') virtualbox
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package virtualbox is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'virtualbox' has no installation candidate

Also tried:

~$ sudo apt-get install virtualbox-5.0
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package virtualbox-5.0
E: Couldn't find any package by regex 'virtualbox-5.0'
user@user-ThinkPad-X200:~$ sudo apt-get install virtualbox-5.0
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package virtualbox-5.0
E: Couldn't find any package by regex 'virtualbox-5.0'

Thanks in advance,

Catriona