Repositioning cruises are usually in the printed brochures but are harder to find on the lines' web sites. You almost have to look ship by ship (i.e. here are the Alaska cruises, here are the Mexican Riv cruises - the repo must be in between).
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014
Star Clippers: Royal Clipper 2015