Depending on your location, and what stores you have access to, wood chips are generally available at stores like Williams-Sonoma, Sur La Table, and other shops of that nature. They are a seasonal product and most of the stores are closing them out now. I, like others don't really care for the chips, chunks generate more smoke with less work.
Finding wood to smoke with requires resourcefulness. The common woods like hickory, mesquite, and sometimes pecan can be found at Wally World. In Texas, smoking chunks are pretty much available year round. I've found that you need to be tree aware to get chunks of other woods. Know what types of trees are in your area, and keep your ears to the ground to see if anyone is having one taken down. It's easy to get wood if it's on the ground. I have a neighbor whose maple tree blew down a week ago, she hired a crew to come out and remove it. I got a cord of maple for next years smoking and as a bonus, she also had a hickory taken down and I got a cord of hickory as well. Cost to me, nothing except a six pack for the workers, who carried the wood to my house and stacked it for me. In the past I've gotten apple, pecan, oak, pear, peach, walnut just by asking for it when trees come down. If you get to know the tree people in your area, you can get a heads up as to what their jobs are and what kind of wood is available. Usually you can get a few logs just by asking for it, the more you take is less for them to haul away and they are usually more than happy to let you have it.