The purple, rare gems used for creating artifact level Artificing gear appear to only come from companions that have a +Crit in Treasure Hunting.
I can not prove this, but in maxing my Artificing skill, I NEVER got a artifact gem mat from any companion other than Kira and Vette. Not even once in uncountable missions on the way to 400. Kira seemed to get them on a rare occasion.
Also, since Sith Warriors get a +5 Crit and Jedi Knights only get a +1 Crit, it seems that Sith Warriors might have a significant advantage.
Again, this is only my personal experience, so it can't be taken as proof.
Qyzen just found Wind Crystal after about gem missions.