There are several alternatives.
Siku, the German toy company sell a pack of containers. The right, modern ISO style but too small for 25/28mm.
Joal. The Spanish toy/collectable diecast company do containers that are 1/50th scale and very nice. The only snag is they do not sell them on their own. You can get them with container cranes or lorries – both or which are pretty useful scenery in their own right. I bought a lorry with containers pretty cheaply on EBay with the intention of making a mould from one and churning out enough to make myself a container port. I got as far as snipping the pegs off and filling in the holes with which the containers could be stacked but never got around to casting it. Somewhat illegal but as I was not going to sell them and was not going to buy more it was not going to hurt their sales – in fact it might help if you go off and buy yourself some.
Model Railway. I believe a company makes some in resin for model railways, if American this would be 1/48th scale, if British 1/43rd scale and if European your guess is better than mine (and I used to think the model railway world was good for standards – well compared with wargamers they still are). Another company makes transfers for them. I have no idea who, but they were mentioned fairly recently in Model Rail, Railway Modeller or Continental Modeller.
DIY. A pain to do but you can get some corrugated plastic sheet from Ratio/Wills that looks spot on for the sides and if you make one yourself and cast it you could sell it legally. Dimensions are easy, the sizes of containers are very strictly defined and you can get the data on the net. I used to have it but it must be on a back up disc somewhere.
Container ships are big, really, really big but fairly simple shape wise. I think you can get smaller ones – in fact I know you can, I have seen them going in and out of Belfast. A small one would be fairly easy to do with foamcore, card and polystyrene. The only really complicated (ie. curved) bit is the bow and I know how to do that. Block it in roughly with polystyrene, sand to shape and fill with plaster. On the other hand I managed to make the distinctive ram bow of a Battlefleet Gothic starship from card. I am still not quite sure how it worked out.
Big boxy hull. Bow, midships with holds, stern with superstructure (crew, etc.), funnel and below that a really, really big slow speed engine. Probably a single screw but you will not see that so who cares. No cranes unless it is very old or small and built for self unloading. The small ones coming in Belfast surprised me, the superstructure was all right angles. Ugly as sin but easy to model.
The AT-43 containers are nice but seemingly not an ISO size which bothers me more that it really should. To me they are the most interesting part of the game package – which is probably quite sad.
