Punitive squadrons are very good places to find the really heavy first and second class ships like the MOWs. They show up on the 3d world map as the largest ships sailing around (about 1.5-2x the size of your ship). It will also take time for the game to generate the MOWs. Since they're such large ships, they will take longer to create, and thus, take longer for them to appear in-game. You can see this in the Ships_init file as well. A tartane takes less time to generate in game (refShip.buildtime = 10
than a MOW (refShip.buildtime = 140
. Those files determine how long it takes for a new ship to be generated, so for every 14 tartanes that pop up in game, there will be one MOW. You can try playing around with these values to make the ships more or less common depending on your preferences. I changed these for some of the new small ships (like the yacht) since it was annoying having my fleet (Arabella, Blue Bird, Dog of War, Sea Wolf, and Soleil - all acquired legitimately) being attacked by Gentlemen of Fortune with tiny ships.