To bootstrap a DU4 non-global zone you need to edit /etc/apt/sources.list and copy sources below (do not forget to make the backup of original sources.list of global zone: sudo cp /etc/apt/sources.list /etc/apt/sources.list.orig):
deb http://10.20.60.188/dilos4 du4-unstable main contrib non-free
deb httpshttp://apt210.20.dilos50.org188/dilos dg2-unstable main contrib non-free
...
IP value shall be unique for each zone.
Do not forget to revert the changes in the sources.list file when a non-global zone has been installed (sudo cp /etc/apt/sources.list.orig /etc/apt/sources.list).