I've gotten them 3 times over 33 runs. I wasn't trying to farm it either. Sucks you can't get them. In year one I felt there was more to the loot table RNG than just the percentage it could drop then s roll. I felt there were loot tables based on player being allocated to a group which made more sense when someone like me got 9 NLB and 6 gallys. While a friend got 12 hard lights and 8 thunderblords. Now in year two it seems it's still occurring. I've already gotten 7 hawk moons while one "unlucky" player got 18 hereafter and another poor bastard got 24 invectives. Not sure if you have done this but some people swear that running different characters can help. I know for me the three I've gotten were not on my Titan. Good luck!