You get the Pixie Queen [Fairy] from Smogger in Katz Lab in Marleybone. Smogger is a secret boss that you get when you go to the Katz Lab [Where you must defeat the guy himself]. After defeating him, run over to the highest platform available and there should be a opening in the wall. Walk over around the wooden planks and it says: "Hmm...We need some wooden planks to bridge that gap." [Or something along those lines.] So, get the wooden planks and return to the opening and defeat Smogger. Let's hope you get lucky. :) Also, it is rumored he drops from Meowiarty in Big Ben.
I really hope that helps, because the pet is TOTALLY worth it. :D -Amber Rosepetal