packing materials
TK Projects (Tom Kedzie) is who I buy pre-perfed cardboard shipping protective corner covers from, in the Chicago suburbs somewhere.
I have an 800 number for hiim- let me know if hard for you to locate.
I have seen reusable shipping containers somewhere but I've never been able to justify the cost myself.
I have seen nice DIY shippers that come from a company I buy linen liners from. They basically 45 degree miter 1x2" lumber and nail them together like a picture frame. Top & bottom get 1/4" plywood, 1/8"melamine or masonite.
For stuff I or customer delivers with reasonable care (doesn't leave your control), I use the preformed cardboard corners and cut cardboard sheet to fit the framed art. Front only or front & back, put corners over the 'sandwich' and tape to the cardboard sheet to prevent coming off during transit.
ULINE has smaller boxes suitable for framed art too. The sizes I 've seen have never been practical for me because they tend to be 'standard' which I rarely see in practice. Take a 'standard size' photo and mat it and it's not standard anymore.
Some suppliers call these 'one-piece folders'.
There is also a flexible form of corrugated cardboard that comes on rolls. Comes plain or (no idea where to get this) precoated with rubber cement, roll & stick after wrapping around the object.
A box making company might be able to sell you flat sheets or roll material, depending on quantity you need. I had to buy a 500 sheet flat...took too long to use up.
A shipping/packing place might be able to help you with quantities smaller than the box maker, if the 'standard size' ones don't work for you.