I tried foraging in all the zones (ranger with machette). Tenebrous is the only place to go. The other zones might be 1 every 30 min. I got 5 in 5 minutes in Tenebrous Mountains
I went to Shadeweaver Thicket off POK and picked up 1 in 30 minutes. Decided to try the other zones. Crossed through Shar val into Hollowshade moors and in 30 minutes picked up an additional zero. Quickly moved on to Grimling where I repeated my 0 in 30 minutes. Ended up in Tenebrous where I got 3 in the first two forages and after 30 minutes I had 8. So my suggestion is Tenebrous. Good luck.
Can anyone confirm that these are actually foraged in Dawnshroud Peaks? I've foraged there for many hours and saw tons of wild crimson berries but not a single wild blueberries. Is there a better zone to forage these?