How can I farm Legendary Weapon Shards now?

So before the patch I was able to get these from Empress Instructors, but since I can't really do that reliably anymore, I need another way to obtain them, and I really have no idea what else would drop them at a decent rate.

Things like this:

If anyone's curious, they're an ingredient needed to create Sengoku Weapons that Madman Ranmaru drops recipes of.