You can also get more generic period ships (e.g. sloops, corvettes, frigates, civilian ships, sidewheelers, etc.) from the Figurehead 1/2400 line at Magister Militum.
What are you playing? I don't understand how you're running out of room on a 3'x3' table with 1/1200 miniatures. Are you using a literal 1:1 ground scale?
Most of my ACW naval gaming has been in 1/600 scale and could almost always fit comfortably in a 6'x6' space (which is to say: we usually *start* on a 5-6' x 8-9' table, but the action all takes place in less than 6'x6' – often *much* less).
Value my advice as much as you paid for it, but I highly recommend sticking with 1/1200. The variety and visibility of the miniatures is much better. Most 1/1200 ACW warships are already pretty small (around 1.5"-2" long), and there are plenty of even smaller ones. I've found most of the smaller casemate ironclads and small gunboats have almost no presence on the table (no masts, low hulls, short length) and are difficult to manage. In 1/2400 scale, most warships will be fiddly and indistinguishable, and only the big broadside warships (sloops, corvettes, frigates) will be longer than 1". If you're trying to do battles like Lissa or Mobile Bay this starts to make sense, but for most riverine/littoral ACW battles with a few small- to middle-sized ships per side, there won't be much to look at and the measurements will be painfully tight and millimetric.
- Ix