Note: There's much cheaper places to buy these boxes, but you can get an idea of what  sizes they come in.      (The one in the photo of my truck is a Continental)
The places listed below sell Dog Boxes, but don't have Web Sites (to my knowledge)
Mullin's Dog Boxes:           Ken Carnsew is one of the dealers for these.
                                        Phone:  330-637-5118      Call him for a brochure.

Country Boy Dog Boxes:   Bill Boatman & Co. sells these boxes (and  other supplies).
                                        Call 1-800-833-4518 for a Catalog.

Fiber Pro Dog Boxes:         Call 1-800-536-4604 for a free Catalog.
This place sells  Uplander and Houndsmen Deluxe Dog Boxes