User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-178.104.172.95-20130412115505/@comment-7584137-20130412124110

I had no problems getting it from Brachy. Usually you get at least one by carving him or in the reward screen. And yeah, I think they are Brachy only, since it is the only monster that uses the Slime ailment.