there is a canadian company called "don't shoot me" that sells blaze orange products for horses, riders, and dogs, originally intended for deer hunting season but good for road work as well.
There was a "pass wide and slow" campaign started in Ontario after eventer Jessica Ruppel was hit by a vehicle riding on the road, causing the death of the horse. A good poster was made up that expalined the laws and proper safety for riders and drivers, and distributed to alot of businesses and to vehicle/driving licensing offices. It was also being discussed to add it to driver training. If you are concerned a similar campaign for your area is very doable. If you post over on EMG forum someone there can probably email you a copy of the flyer to give you inspiration (your road laws may be different).