Greens, or nitrogen-rich materials, are often easy to come by. When using an outdoor compost bin, many people have trouble locating enough browns to maintain an appropriate nitrogen to carbon ratio. Here are some suggestions from one our Master Composters for locating some local browns for your pile.
Yard trimmings: dried leaves, wood chips, dried plant trimmings
Chipper/shredders: can be a great investment, especially if you have a lot of wood to chip.
Local tree trimmers: Befriending a local tree trimmer and getting loads dumped of predominantly wood chips is a great method of obtaining browns. Some tree trimmers chip everything, including massive trunks and they will often bring it right to your residence.
Straw: which is mostly carbon, not hay which has much protein (nitrogen/green) and is expensive.
Shredded paper/cardboard: If you are using very fine greens, paper and cardboard can often get too compact and dense for appropriate aeration. It tends to work best if moistened before added and used with materials that provide good aeration like wood chips.