@fronttowardsenemy is right. Easiest way to plug in to find herb or anything else is to talk to locals. Bartender, fast-food restaurant workers cabbies, bellhop, and tip a cool person.

Avoid anyone that's stressful or paranoid. Never hand out money first.
Never buy without checking.
Be careful of multiple people who are in on your deal. Just your bag. No group order if you don't know them.

And know your source. Trust goes both ways.