i can tell you where i got mine. i got the life (green) or healing pixie from smogger . in kenzenteins lab ,in marleybone. i got the(brown) sprite from prince alicane swiftarrow on firecat alley in wizard city cyclops lane. and the dark fairy from lord nightshade haunted cave. hope this helps you! :-)
That pet is dropped by Smogger who is a secret boss in Marleybone. I don't want to spoil it too much by telling you exactly where he is though. You might ask around while you check all the dungeons and stuff though.