Comment 2 for bug 1394088

I feel your pain! Considering Mono is now on 4.x it's a shame the current Ubuntu package is so old.
I rely on the Mono repo to stay current:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb http://download.mono-project.com/repo/debian wheezy main" | sudo tee /etc/apt/sources.list.d/mono-xamarin.list

Only run if Ubuntu>13.10
echo "deb http://download.mono-project.com/repo/debian wheezy-apache24-compat main" | sudo tee -a /etc/apt/sources.list.d/mono-xamarin.list

Finally

sudo apt-get update

Source: http://www.mono-project.com/docs/getting-started/install/linux/#debian-ubuntu-and-derivatives