This is a tough one. For a start, try Taubman Plans Service. Abe Taubman is the best dealer in the U.S. when it comes to ship plans for model builders. I don't have his address, but you can get it via his ads in Ships in Scale magazine. That publication has a website: <www.seaways.com>. Taubman Plans Service in fact has a website of its own, but be warned: the list of products on it doesn't include anywhere near everything Abe has for sale. To really make use of his services you'll need to get hold of his printed catalog.
There are no official repositories for merchant ship plans. Some musem archives do have such documents, and some are willing to reproduce them. For U.S. vessels, try the Mariners' Museum (Newport News, Virginia), the Peabody-Essex Museum (Salem, Massachusetts), and the San Francisco Martime Museum. You may be in for a frustrating experience, though; if the archivist you talk or write to doesn't happen to be a buff on the subject, he or she may not know whether anything in the collection fits your interest. For British ships it's worth trying the National Maritime Museum (Greenwich). That place has the biggest collection of ship plans in the world. It does sell copies, but they're notoriously expensive. A letter to Greenwich probably will get you an answer from an archivist who can direct you to other good repositories in England and Scotland.
This is a fascinating, important, and under-documented subject. Good luck.
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