I forgot there was someone in the game that will give you the Reveal Glass if you have one of the three Nature Guardians(Tornadus, Thundurus, and Landorus). I cant seem to remember where. Could you please fill me in?
If your go into reflection cave, there is a female scientist who talks about the reveal glass. If you show her tornadus, thundurus, OR landorus, she will give you the reveal glass.
Hope this helps!
You can find it in reflection cave.