Sadaryx Quality

I am trying to farm some Sadaryx quality for crafting. I have done multiple runs and all I ever seen is 258 and 510 quality. Anyone got the same problem?
Maybe I am not hitting all the spots, but usually leaving with 20+ stones. I am entering via investigation missions. Maybe I need to do exclusive private one for 850k fee to spawn better qualities or whats the trick here? Or just unlucky? Anyone found better quality doing just farm runs via mercenary/investigation missions?