You mean Black2, right? I'm pretty sure that the alternate forms are only available in B2W2.
If you're using an emulator, load your save file in Pokesav and then you can attach the Reveal Glass item to one of your Pokémon. Here's the download link for Pokesav: http://pokecheats.net/tools/pokesav/...%20-%20PSN.zip
You could also use the Online Pokesav to save a .PKM file of a Pokémon that has the Reveal Glass attached to it. You can then load that Pokémon into your game's save file. Here's the link for the Online Pokesav:
http://pokecheats.net/pokesav/b2w2