Here is an idea:

Go to central park and ask every degenerate and shady fuck you see if you can have some free weed because it's 4-20. You'll find out quickly whether that idiotic rumor you heard is true or not. In fact, make sure you ask every dangerous-looking person you see, too.

And even if it is true, Central Park is huge, with thousands of people walking through every day. Can you say, "Needle in a haystack?".