Yes Uline has them will attach the link. They also have deluxe artwork shipper box, boy are they proud of them. But there stander artwork/mirror boxes are not to bad in price. But I'm shure someone else will
know of another place to purchase these boxes. http://www.uline.com/Browse_Listing_7901.asp
watch the shipping prices on Uline - they deliver by truck and sometimes you order the minimum and the shipping is just as much. I went to a local company and had boxes made to size for my larger pieces that I ship - it was more cost effective.
Victory packaging has similar boxes and seem to have wharehouses all over the US and you can usually pick things up if they are near by with a minimum order - I use them for mirror boxes
Find a packaging supply company in your area; not a packing store but a business that supplies packing supplies to businesses. We have one in our area that we buy boxes, packing peanuts and bubble wrap from. They deliver free with a $100 order. Your area may have one also. I use a lot of the ULINE flat boxes and the packing supply company in my area can get any ULINE box. Their delivered price is about the same as from ULINE without shipping so we save the shipping costs. If you use bubble or peanuts the savings is quite a bit as these puppies are expensive to ship.
Being one of these hard headed framers, I build my own shipping containers. If the frames are particularly expensive or you are shipping framed art, it is a very inexpensive and safe method to ensure that your pieces arrive in one piece.
I build the carcass out of the cheapest 1x4's that I can find or rip down larger one x stock to the size that you need. You can miter the ends on your chop saw and join them with PVA glue and bugle head screws. For the sides I use either double thickness cardboard or thin masonite. Every box of foam core has a large sheet of double thickness cardboard in the bottom box and I use a box cutter to cut away the sides and store the bottoms in a closet until I have a need for them.
You can cut them to size on your wall cutter and use PVA and either staples or 1" bugle head screws to attach them. I put one sheet on the carcass, a layer or 2 of bubble wrap in the box until the frame is centered, then place the frame into the box, and fill with more bubble wrap until it is all snug in the shipping box. You can fill around the sides of the frame to keep it from shifting around with strips of bubble wrap and then glue and screw the top on the container and you are set to go.
I have been using this method for quite some years and haven't had any insurance claims to date. It does require a bit more work but that hasn't killed me yet and I enjoy building something that I know will get the job done.