As of 2014, there is a website called Garden Winds that carries replacement cushions, canopies and other parts for outdoor furniture sold at Walmart, Costco and other major retailers. To obtain replacement parts for any store-bought item, however, the best resource is usually the original manufacturer.
Walmart carries a variety of porch swings with attached canopies, including ones by Coral Coast, Sonax, Leisure Season and Moon Valley. Garden Winds carries universal canopies and cushions, as well as replacement parts with names like North Hills, Mainstays, Sand Dune and Palm Valley. If an exact match of replacement parts is not in stock, it is important to find the replacement parts that best match the swing to ensure safety and ease of repair.
For some parts, the manufacturer must be determined. If the swing is old, does not have its original box and isn't marked with an identifiable brand, a trip to the store where it was purchased or an online search may help find a comparable model. Once the swing brand is identified, the manufacturer may be contacted to see if the item is under warranty and whether replacement parts are available. If not, a hardware store may carry the pieces needed for a mechanical repair.