Howdy Scottie,
CARDMODELS TO THE RESCUE! lol, Why Buy the containers when you can print off your own? Check out this link for containers of all sizes.
http://home.wanadoo.nl/schatborn/
Here you will find paper models of containers like you would find on ships or on train flatcars anywhere in the world. See the photos below:
20 ft containers:


40 ft single containers:


40 ft "4 in 1" container models:


Anyway you get the idea..... here is a photo of the actual models completed:

sorry its so small, thats the was it was on the site.
The good thing about cardmodels is, you can scale them to the size you need with any photo editing program, if you mess up, you print another, and last but not least, the only expense is your paper/card stock and ink.....a whole lot cheaper than buying "boxes".
I hope this has been of some help to you, have a good day,
Greg
ps, I keep telling ya'll that "if you can think of it, theres probably a card model of it".
Try testing me sometime on this lol.