Zenith Harbinger Skin
Sounds like a bug. I am assuming you scrolled through all the choices available. And that you haven’t chosen it before. (Skins are only available once per day.) You can report this in the Game Bug sub-forum, if needed. =)
Skins are only available once per day? Per character? I didn’t know this!
It’s also possible, OP, that you need to scroll the window if it’s full. Some stuff might be on the second page.