Look for a Goodwill outlet. They take all the unsold stuff from their other stores and just dump it all helter-skelter into giant bins that you can paw through; clothes are sold by the pound rather than by the item.
I was told that anything that doesn't sell from there is packed into tight bundles and shipped overseas to 3rd world countries. I always wondered how kids in African villages ended up with old weird promotional tee-shirts; now I know!