How to download all repository using apt-get?

First of all, this is not a convenient way. Instead of this you should use the method mention here. But as an answer to the question.

• First create a file which contains names of all the available packages using apt-cache.

  apt-cache  dumpavail |grep -oP "(?<=Package: ).*" >> packagelist
  

  This will create a file packagelist with all the available packages.

• Now create a simple script to download all the packages present in the file packagelist

  #!/bin/bash
  for package in `cat packagelist`
   do
      apt-get install -y --download-only $package   
   done
  

• Save it.

• Make it executable using

  chmod +x your_script_name
  

• Now open terminal and login as root

  sudo -i
  cd /folder/of/you/script
  ./you_script_name
  

It will download all the available package depending upon your /etc/apt/sources.list in /var/cache/apt/archives directory