I want to add civi hr extension to drupal. But is not available in drupal.
You need to first get into the extension directory, and download the extension directly. Then you can install the extension from Manage Extension Page.
wget https://github.com/civicrm/civihr/archive/1.3.0.zip unzip 1.3.0.zip mv civihr-1.3.0 civihr
You can now move to
Administer>System Settings>Manage Extensions Install CiviHR and you are good to go.
This link can help you further.