Similar to Veggie Trader, Neighborhood Fruit (still in beta) allows you to track down people to share fruit with locally. Not only does it list people willing to trade, but also lists trees growing on public lands (there are already 10,000 registered trees nationwide!).
After creating an account, Neighborhood Fruit gives you access to all registered trees nation wide. You can add your own, or just see what's out there. Upon inspection, it looks like New York City and San Francisco are doing well for public access trees.
So get out there and find a neighbor with some fruit to share!
See also Your Local CSA.