Addons are earned in a unique way. They are given to you kinda like a milestone reward for your level. I will be updating this site once i find out which addon comes with which level. so far as i am only 175, i only know all the addons up to my lvl.
These are all the addons you get per level. It is a rumor that at lvl 275 is when u get your last and final addon. But until someone gets it we will never know :O!