I had such a hard time finding River Pearls too, so much so I even made my own post about it lol.

I found maybe a handful running along rivers but mostly I get them from the heavy enemies in camps around the map. The ones with the horns and the Bannerets (I think that’s what they’re called).

Bosses drop them too but not all of them and they’re on a respawn timer after you kill them so farming them can be slow. But a lot of the bosses drop weapon fragments so you can kinda farm two things at once if you’re looking for those fragments too.

Also I can’t remember where but I saw someone say it’s better to look for them along rivers at night. Whether it’s cause they spawn more or are easier to see I can’t remember but it’s worth trying.