Install the old client: https://launchpad.net/l2tp-ipsec-vpn
First install required packages:
sudo apt-get install gksu libgksu2-0 libctemplate2 libengine-pkcs11-openssl libp11-2 xl2tpd
Next download the old binaries and install with dpkg:
wget http://mirrors.kernel.org/ubuntu/pool/universe/o/openswan/openswan_2.6.38-1_amd64.deb
sudo dpkg -i openswan_2.6.38-1_amd64.deb
wget http://mirrors.kernel.org/ubuntu/pool/universe/l/l2tp-ipsec-vpn/l2tp-ipsec-vpn_1.0.9-1_amd64.deb
wget http://mirrors.kernel.org/ubuntu/pool/universe/l/l2tp-ipsec-vpn-daemon/l2tp-ipsec-vpn-daemon_0.9.9-1_amd64.deb
sudo dpkg -i l2tp-ipsec-vpn_1.0.9-1_amd64.deb
sudo dpkg -i l2tp-ipsec-vpn-daemon_0.9.9-1_amd64.deb
Open the client. Add a connection and configure as needed. Once you try to connect it may take awhile but be patient.