I googled the ship and the details you already have are easily available. The owner, builder etc info is available if you register with the site. Once you know who you will need to make contact as Haverlock advised.
Depending on the scale detail you require you may only need outline hull plan drawings with perhaps a side view to add the superstructure.
Looks an interesting model. Ballast will be a major problem.
I have built several large models and now consider the best solution is to make a sealed fore and aft section with the centre being open. The buoyancy is only provided by the fore and aft sections. I need 50Kg of lead in my 9' Olympic and I suspect you would be looking at possibly much more in this model.
I take the view that I am not carrying any cargo so don't need the hull capacity. Once on the water the model will look correct and be easily transportable.
Good luck with your search. A build blog would be very welcome.
Dave 😀

Presumably, if you are going for N gauge you do not require too much detail. Consequently, all you would need is General Arrangment drawings. I would think that photos are more important.
Good luck and let us all know how you get on.

Your first port of call should be the builders. They hold all of the plans for any vessel they have built.

if you haven't that data contact the owners they can advise who you need to contact.

They will probably charge to copy these plans for you and there can be a LOT of them.