I think the easiest and least expensive way for you to add more ships would be to use similarly-scaled vessels from either Panzerschiffe or Navwar…
…and paint them. Unlike the A&A WaS miniatures, the minis from both companies are still in production, so you won’t pay a collector’s premium for them. The Panzerschiffe ships have the advantage of being cheaper to get (they’re made of resin, and the company is US-based), while the Navwar ones are more detailed and are made of metal. There’s also GHQ (http://www.ghqmodels.com/), whose models are even more detailed, if that’s a consideration for you.