All of the free Millennium Horse stuff that I managed to find was through Mystic Nights' data base by searching "horse".  You can also search for the specific item like "Saddle".

http://mystic-nights.com/directory/index.php

HaiGan used to have a whole bunch of horse stuff in his free area here, but they were removed.  You might try searching his name and sending him a message and ask him about them. I think his stuff was for the Poser horse, but with resizing and parenting Poser horse stuff can work with the Millennium Horse.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi