We do plan to add Transmog Vendors ingame, but these vendors will only be selling items that are unobtainable because of certain circumstances (such as instance not working, creature is not there, etc.). Now to make this be more faster what you players can do is, make up a list of items that you want to have but can't get because it is unobtainable. Please note that I will also be researching the items you put in your list too, so that I can know whether or not the item is really unobtainable or not.