Buy another mini or a shapeway model

Vainamoinen is about $2 on eBay. I think with affordable minis like that, people trend toward the Wizards mini.

I have both. Plenty of original ships for sisters, but I also have bought a lot of Shapeways as the minis tend to be better quality and look better when painted up.

I started the game when it first came out so I have enough of the "rares" to cover most of the sister ships of carriers and BBs and lots of all the rest (but not to class limits.) Buying and painting sisters of the WotC miniatures is a low priority for me, but I have done some of them, especially if they are the very expensive and hard-to-get rares like Massachusetts, Graf Zeppelin, etc. I like to do those just to increase the general "pool" of those miniatures in the wild.

Getting one WotC miniature also gets you one card. After that you are probably using the fan decks and I think the 3D mini's are nicer if you are willing to paint. But we do provide the "closest WotC proxy" lists if you prefer to use the WotC miniatures exclusively.

And you might even have a suggestion on where to find the ships.....

Like Weeds, I was in the game from the start. Only went the other way, often picked up a fair number of duplicates to use as sister ships. I wasn't sure the game would last (Ha!), often leaving a slot or two open just in case a specific miniature came out later.  I was one of the first at the door whenever a new set was out, raiding Miniatures Market while the prices were low.  Did my best not to have more of any class than actually starred in the war (and totally avoided the Soviet fleet! and fantasy ships) but to do that, could only buy one or two boosters per release before switching to individual unit sales.  In the latter releases, the cruisers, battleships, and carriers (especially carriers!) as individual minis started getting expensive fast so in some cases, then I bought an earlier WaS duplicate and just re-tasked it. That saved some money.

I had the advantage over many players in that I could re-create the cards and modify the names so that I had cards matching the intended sister ship so cards were never an issue.

I was a bit slow to gravitate to the Shapeways market, leaning a bit toward being cheap, some of those Shapeways miniatures are expensive!  I didn't mind painting so that was OK but sometimes it would take me a while to paint so the ship may be "in dry dock" for a while.  I started buying ships that had no representatives in WaS, and filling in some of the gaps.  Some of the Shapeways models are especially nice. Only recently have I started actually replacing existing WaS models (the entire Country class, now painted in either 1941 or 1942 colors for the most part, and the entire Atlanta Class). It really depends on the class and the mini.  For you average unit, there is nothing wrong with the original WaS miniatures, especially for gaming.  If you are trying to save a bit and can get a good deal, as Weeds points out, you also get a card with the WaS minis, even if it doesn't have the sister ship name on it.  If you think it is a cool class of ships, or the models are especially nice (I can't resist Tinythingamajig's minis), or show some differences actually reflected in the Shapeways models, go for the Shapeways mini.  In the end, my Shapeways minis are generally my favorite but that might be because the extra work that goes into them makes them a bit special. 

Right up until Covid put out a mine field, the San Diego Group had been meeting nearly every Monday night to play a game since the fall of 2007, even if the group isn't especially large these days.

I do. I vastly prefer XPForge as a vendor over Shapeways. They maintain similar or better quality but are cheaper and have better customer service. (Linked is the Ilmarinen from the original question.)