WFDU, Teaneck, New Jersey (89.1 FM) programs a fair amount of folk - and country - music. They reach well into the New York City area and beyond. They have a regular feature called the Music America Concert Calendar, which gives brief descriptions of upcoming folk/country activities in the NY - NJ area.

I'll repeat the suggestion posted above - how about posting the details of your event here. It would help if we knew the exact when-and-where info.

Note that we're talking about PSA/community calendar type listings here. Actual advertising would require approaching a commercial station and paying them too much money, which would be wasted, since that's not where folkies go to get their live concert info.

Regards,
John