I'm with most of the other guys here – when you say "coastal", I think 1/1200 or 1/600, since a lot of the coastal vessels were small. In 1/1200, most MTBs will be around 2cm, most DDs and escort destroyers in the 5-7 cm range, and coastal cargo ships mostly in between those sizes. Obviously, 1/600 models would be double those sizes.
1/1200 boats are just a tad on the small and fiddly side for MTB gaming, and 1/1200 DDs are just a bit oversized for their speed and gun/torpedo ranges, but 1/1200 is a nice compromise scale for either. It's the scale I will personally go with if I branch into this period, just so I can leverage all my existing shore terrain, markers, accessories, etc. Allen57 already listed the major outlets I know of for 1/1200 coastal forces.
1/600 miniatures are nicer to look at, easier to handle, less fiddly in gaming operations than 1/1200, and therefore generally more fun for naval gamers to play with. They're big enough that you need larger tables to have enough maneuver room, especially if anything DD size or larger is in the game. Allen57 already mentioned PT Dockyard, the new Heroics and Ros has the old H&R 1/600 coastal miniatures lines, and you can also shop the 1/700 scale plastic model manufacturers for cargo ships, planes, and larger (DD and up) warships. I'm sure there are other options, but this isn't my period, so I'm not much help.
- Ix
PS: Hallmark was the company that made all the Figurehead lines of miniatures (in 1/6000, 1/2400, and 1/1200) before closing its doors and selling its lines to other companies like Magister Militum and Noble Knight. (Incidentally, Hallmark also made a nice line of 18th C. 15mm stuff that included some naval guns).
