There should be other ways to obtain the Field notes.

[Coulvre]

Now I'm thinking they could do something akin to a pity system in gasha game. The more you do fates, the closer you get to the pity. It could be like 100 or something. At least, we can count while praying it drops before. But then bam, we hit the mark and it drops.
Currently, it feels endless.

Notoriety works in a similar way to this so I feel like it shouldn't be too difficult. I agree with what everyone is saying, I would really like to see another option to get the rare ones than RNG and duels.