the entire series is currently free on Amazon US so get your free copy and enjoy :)
Volume I - http://www.amazon.com/dp/B00AX19RAA/
Volume II - http://www.amazon.com/dp/B00CIGKCFC/
Volume III - http://www.amazon.com/dp/B00G0NN7QA/
Volume IV - http://www.amazon.com/dp/B00KUIZELW/
Omnibus - http://www.amazon.com/dp/B00DZ71QQ2/
Nice find, OP. By the way, Omnibus appears to be vol 1 & 2 combined so can be skipped if you pick those up.