Anywhere - FallingFruit.org lists public places to go out and pick your own produce that might have otherwise gone to waste.
U.S.A. - there are many gleaning groups but the U.S. Department of Agriculture (USDA) is a great resources to start with (that even includes grants to start your own program) and the Society of Saint Andrew is one of the biggest gleaning organizations.
You can also check out the National Gleaning Project from Vermont Law School.
While you can go to the farmers market, corner store or some grocery stores to save "ugly" produce, gleaning exists all around the globe. Gleaning is the time honored tradition (which even is spoken of in ancient religious text) of gathering a group to harvest produce that's left in the field for various reasons. You'll find some gleaning resources below but, if none of them help you, just talk to local food banks and pantries to join in on their gleaning efforts.
You can also ask farmers (maybe even at your local farmers market) and see if they know some gleaning groups or will let you glean on their farm. Some farmers even have gleaning adventures for everyone! Food banks and food pantries also work with gleaning groups everywhere so you can ask them as well. Let's not let as much as 40% go to waste for cosmetic reasons while 800 million are food insecure, go gleaning!