Aside from SC&H, there are no kits. Plans for various vessels can be had from various places - I think there's a thread in this forum listing a couple of sources. The National Maritime Museum can supply you with copies of original draughts, build orders, materials lists, etc for nearly any British vessel you can come up with - but you will pay dearly for them.
Building from scratch is not more difficult, it's just like building from a kit except you have to make all the parts the kit supplies pre-cut. It's generally cheaper. As mentioned, the plans can be steep, and fancy materials can get expensive; but I don't have more than $400 invested in
Constellation including radio equipment. The cost of scratch building can also be spread out over time - whereas a kit you have to pay for it all up front. (usually)
You might take a look
HERE for a little inspiration.
Here are three large models I have in the works:
USS Constellation 1:36 scale. Sloop of war built 1854 and still exists at Baltimore Maryland USA. Plans from US National Archives.
HMS Macedonian 1:36 scale (
a build log in this forum)
Lively class frigate built in 1810 at Woolrich. Plans from Smithsonian Institution.
Pride of Baltimore 1:20 scale Baltimore Clipper tops'l schooner replica as she appeared when I sailed her in 1981. Plans from designer Tom Gilmer back in 1982.
My site details their constructionCome on in - the water's fine.