For the rest of New York City (boroughs outside Manhattan) and NJ you'll need to post on the appropriate non-Manhattan boards.
For Manhattan sources, check the Greenmarkets. In the past Mountain Sweet Berry (Union Square Weds and Sat) has carried it. You can actually reach out to the Greenmarkets directly via Twitter; the accounts are pretty quick to respond.
You might also want to keep an eye on Lucy's Greenmarket Report: