Rather interesting that it mentions “small chance” from Eveline, as in the current state of the game more than half of all crystals come directly from her. Eveline over the course of what is needed to max all followers would have produced more than all side quests combined.
She is the primary method, but it isn’t mentioned as such.
Only Eveline, but it would likely be only Eveline regardless of if every crafter made them or not due to level of follower potentially effecting the drop chance. This is due to it taking around a year for another crafter to reach level 50 (Toragon), and even if both were level 50 probably best just to stick with Eveline.
The ruby/diamond keys off Eveline also get an additional chance for it too.