I know this doesn't help much but I was able to find some on the beach in dig sites.
languid void
I know this doesn't help much but I was able to find some on the beach in dig sites.
I bet as we get deeper in diving that silver kelp will appear.
verbal beacon
Silver kelp is plentiful in the second diving area that you unlock after the initial 20 beacons. Trust me, there's plenty. Before that, though, its just digging on the beach and chests.