How to get drugs 101. This will work with near certainty if you're a girl, and has a good chance of success if you're a guy, as long as you're not a flaming sperg or just extraordinarily creepy.
Live near a college or university.
Travel to said college during the day. Bring $100-$300.
You can actually literally start asking people for weed at this point, but you won't need to.
Figure out where the frats are. Go over to one of the frat houses.
Just walk in, or approach people chilling outside. Be confident, and say something like "yo I'm a grad student here, I was trying to buy an oz (pronounced "oh"), my buddy said you guys smoke a lot, is anyone selling in this house?"
This will not always work. If the fratbros you talk to turn out to be douchey types, they might turn you away. Don't be too insistent if they say no. If they say no, ask which frat is the stoner frat, or ask which frat you might have some luck buying weed. If you strike up a decent conversation, you can also just ask them where they buy their weed. If they're rude and douchey and dismissive, walk over to a different frat and repeat.
Things that help: looking like a college student, being dressed like a college student, carrying a longboard/skateboard, wearing a baseball cap/beanie, being dressed casual but not creepy, being able to talk to people and seem chill and normal.
Creepy method: Go to college at night and walk around the dorms. If you're lucky, you'll spot a group of dudes smoking weed. Approach them with the same shtick about being a grad student and trying to find weed. Chances are they'll give you their dealer's name.