I assume you asking specifically about HORIZON boxes.......most all of the boxes are going to be the same because they are designed for shipping birds. Otherwise, we could just put em' in any old box.......here's a couple of places that aren't HORIZON boxes, but are approved for shipping and probably a bit cheaper.
http://www.boxesforbirds.com/index.html
http://poultry2.tripod.com/id3.html