Yeah AFAIK they're just random drops
You can farm Challenges for them, probably the most direct way (though still pretty tiresome). Go to Kobold Island, kill the red name by the large collector, you'll get a chest in your inventory. Recall, repeat until you have a lot of chests. Open them all, and you have a small chance to get an Augment (as in every random-loot chest). You can also control the level of loot that way, though the chest level isnt the same as the level you set the challenge to, so you'll need to calibrate it first
You dont have to deal with ransack like you do farming easily-accessed chests in quests, either.
One thing working in your favor is Dodge is usually a trash stat, so its likely they'll appear on the AH as soon as people start finding them. Or...they wont, because people will just delete them since Dodge is a trash stat