What the, where'd you hear that?
Not that I know of. They are the rarest things so you just have to keep trying. Also, you can get dupes.
You have to go to a stable that has customization options. Not all of them have it. I think Highland is one that does. There will be a person standing near the horse stalls who can change the look of your horse and change gear for it.
If I did the first bit of DLC, and now I'm into the second (I think something to do with the Champions?) after doing the one-hit-kill shrines, what is there after that? I think I need to do some more of the actual game too.