Hi Kristal - I get a lot of my boxes (and packing peanuts) from local manufacturing companies and from the local hospital. The boxes are all free, and I have formed a relationship with these places, so they now save boxes and packing materials for me. I just pick up a couple times a week. If you look for local manufacturing companies that are ISO certified, they cannot reuse packing material, so they have to throw it out. It's always clean and used one time - perfect for me.
When I'm in a hurry and need something specific, I order from Uline (it's next day delivery for me). I think their shipping prices are pretty high, but when you need a specific size, it's worth it.
JD