I have run siegebreaker at least a dozen times and have as of yet to get one. I was getting ready to run it again after checking the message board.Have you tried farming them? They drop in any chest in Siegebreaker. The kobold in the beginning spawns pretty quickly after only clearing the room—gank rinse repeat gives you 8 shots at it. You can burn the tents and poison the water supply—all right nearby—for two more chests x 8.
Some named items there drop in the chests too so you might get some sentient food in the meantime.