Rear Facing Horse Transport has proved itself a good option in research studies, and is slowly becoming more popular, its really surprising that it is taking so long to catch on. Some innovative manufacturers do produce them, and many people are converting existing trucks and trailers, like I am, but they are still a rarity at this stage.
Research on Rear Facing Transport
Studies by University of Carolina and University of Edinburgh:
http://www.mdhorseboxes.co.uk/rear-facing.html
Review of older research into rear facing:
http://www.j-evs.com/article/S0737-0806(82)80025-7/abstract

Rear Facing Horse Transport Manufacturers
Equibalance in NZ:
http://www.equibalance.co.nz/
Balanced Ride Trailers in the USA:
http://www.balancedridetrailers.com/
Equitrek Trailers in the UK:
http://www.equi-trek.com/au/horse-trailers/space-treka-m
Other Aussie DIY Conversions to Rear Facing
A Rear Facing Truck Conversion by Glenn Wilson:
http://www.waterfallcreek.com.au/Open-Attachment/69/Just%20to%20be%20Different.pdf
Another Rear Facing Float Rebuild blog by Suzanne Bellette:
http://rearfacing-horsetransport.blogspot.com.au/