Actually, the number of merchant ship kits between about 1/500-1/400 scale is pretty decent - even more so, when you drop in the additional caveat "naval transport/cargo types". Many of the molds have changed hands over the years - and were reboxed as (whether accurately or not) as different subjects , so that the number of names to search for can become quite large.
Here's what you do:
1) Go to "RAJEN'S LIST" - it's long; wait for it to load completely - so pick a long, lazy weekend; when you can browse it for merchant/transport subjects under the following MANUFACTURERS listed there:
These half-dozen manufacturers have, over the decades, sold their molds to maybe a dozen other brands (most of them in Eastern European, ex-Eastern Bloc countries), some of whom are still producing these kits today. And yes, Revell DE is doing exactly the same for a couple of the Revell classics, as well.
Familiarize yourself with the codings used on Rajen's List - and check out the cross-links provided - to get a very good idea of what molds were made, under what names, and what subsequent names/brands where you might find them - maybe even in production - today.
And then, plug those names into a series of eBAY searches. If you're not familiar with how to do that, we can help you out there, too, buddy.
I'll let you try your hand at the above and get back to us with your next question(s), to see which way you are taking this, and where you might need a hand. (And also, to see what gold mines you can scare up for us!)
Oh - and BTW, it's a little larger than 1/400, but check out what I was able to do using the Trumpeter Jeremiah O'Brien kit.
Again, great to have you aboard ModelFleet, Jim!