Saber Drop Rate From Junk

Does anyone know if it is level-dependent or triggered by beating the dragon once or multiple times? I have farmed out over 30k currency but never beat the dragon yet, and I'm only level 30. I have yet to see a single saber in around 600 junk piles. Am I just having horrible luck or am I missing something?

I keep hearing and seeing that people are getting them all the time, like 1 in every 20 piles of junk. I feel like the junk piles that drop the saber just aren't available in chests at level 30.