Where do I find mount accessories in world of warcraft?

Ok, I'm a human mage with a mount. Now, I have seen mounts with armour and mounts that blaze and I know that some of these things are class specific. But I also recall seeing mount accessories somewhere. I just can't recall where. It might have been in the auction house. But, if that was the case, it isn't there now. Are there quests that you have to do to get accessories or can they be purchased from a vendor? I just want to make my mount look unique or cool.

The Golden Armored Horses are Paladin Special mounts, The "fire Steeds" are a Warlock special mount. If you want a black mount you need 30 of each PVP marker and the epic ride skill and you can buy it from the pvp vendor. as for "Items" to make your mount look cool or different, there is no such thing.