Anywhere in Luclin, excpet for the Bazaar, Nexus, and The Grey. Best bet is Shadowhaven or Echo Caverns because of few or no competing zone specific forages.
ive noticed people like these. i foraged for a stack of the today (took about 1 1/2 hours!) and sold the stack to a person for 10pp. i dont know, maybe the guy was low on food but, all i know is i made 10pp off of mushrooms!