I have occasionally tried exploring this...
The big question is, do you want them for combat as per the rules in the book or for the looks of it? I think trying to fit the unit bases onto a ship is such a pain - for me I only ever thought of ships as like markers, something to pretty up the side of a battlefield or to represent when reinforcements / evacuation is coming to a beleagued army!
The Dreadfleet Empire or High Elf ship are obviously an option from eBay, but they are pretty much ultimate capital ships, the most powerful vessels in the entire Warhammer world rather than the kind we would use.
There's obviously the old Man o' War ships. Around the old World the more regular Bret and Empire ships might work but I've not seen them in person to see if they scale up.
In terms of modern models, I think this is the best thing currently available:
http://www.ghqmodels.com/store/napoleonic-micronauts-battle-sails.htmlI'd really like a coastal terrain section using these kinds of things as wrecks.