Accessories for the mane for horse shows are more easily found if you can be more specific about the type of horse show accessories for the mane you are looking for.
One type of horse show accessories for the mane is braiding bands. Braiding bands are the most common horse mane accessory, and are appropriate for most shows. Braiding bands are tiny rubber bands used to braid the horse’s mane. Braiding bands come in every color horse manes come in, and also come in colors like clear, metallic silver, metallic gold, and even bright fluorescent colors!
Another type of horse show accessories for the mane is flowers, of the sort used on draft horses in draft horse shows. Draft horse mane accessories for horse shows can be found by searching for "draft horse show supplies".
Another type of accessory for the mane for horse shows is spray on glitter. But caution! Glitter is not appropriate for most shows. Horse mane glitter is only appropriate for parades, demos, or just trail riding. Most shows prefer a more traditional appearance.