mkdir source; cd source

#!/bin/bash
dpkg --get-selections | while read line
do
        package=`echo $line | awk '{print $1}'`
        mkdir $package
        cd $package
        apt-get -q source $package
        cd ..
done

chmod a+x getsource.sh

./getsource.sh

apt-get source package-name

#!/bin/bash

# ${Source} doesn't always show the source package name, ${source:Package} does.
# Multiple packages can have the same source, sort -u eliminates duplicates.
dpkg-query -f '${source:Package}n' -W | sort -u | while read p; do
    mkdir -p $p
    pushd $p

    # -qq very quiet, pushd provides cleaner progress.
    # -d download compressed sources only, do not extract.
    apt-get -qq -d source $p

    popd
done