User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-31.120.57.88-20130405171329/@comment-86.3.144.81-20130405172005

I got my first one from gobul, however I think you can get them from any large monster which does not have a gem/ruby of its own: like rathalos or uragaan for example. I did get TWO wyvern stones on my first run of the black diablos and diablos high rank quest (9star quest called 'Triumph of the Tyrants', so maybe it is more likely to get them from the quest. Good luck finding them!