Nirncrux show up [rng] from wood, ore, and fiber nodes, or things that will give you "fiber" items. I was rather surprised to get one off a welwa along with the leather scrap. Runes and alchemy nodes, no.
Can I get Nirncrux from doing Craglorn dailies?
I have never seen one drop as a reward from Craglorn daily. I have rarely gotten them from harvesting crafting nodes. Folks have claimed online that they have rarely gotten them from killing creatures that drop leather, like Welwa.
Nirn is pretty cheap in the Guild Stores these days. You could farm Gold earning items and buy them.
Now, Nirn does drop from certain Event Reward Boxes, so it can drop from Dailies. I think they are the boxes related activities.
im pretty sure you can get nirncrux from enchanting nodes also