There are several options for purchasing cardboard boxes for shipping.
Online retailers: Amazon, Uline, Walmart, packagingprice.com, and packagingSupplies.com are great options for buying cardboard boxes in bulk. The online stores offer a variety of sizes to choose from, and they offer good discounts from time to time.
Office supply stores: Staples, Office Depot, and FedEx Office all sell cardboard boxes of various sizes suitable for shipping. They may also carry packing materials such as bubble wrap or packing peanuts.
Shipping companies: UPS Stores and FedEx Office locations typically have a selection of cardboard boxes in-store. These stores often have knowledgeable employees who can assist with selecting the right size box for your specific needs.
Local moving companies: If you live near a local moving company, they may sell you some used moving boxes at a discounted price. Before deciding which cardboard box(es) to purchase, consider the size, weight capacity, and durability required for your shipment.