You can get sources at official site but you'll need to install a lot of dependencies to compile it.
Or here is already compiled version:
Download hd-idle_1.04_armhf.deb
Installation:
# cd /tmp # wget http://i.sepa.spb.ru/_/mele/hd-idle_1.04_armhf.deb # dpkg -i hd-idle_1.04_armhf.deb # nano /etc/default/hd-idle