Here's a trick for making cannonballs of any size you like. It relies on trial and error, but doesn't take more than a few minutes.
Chop a piece of brass wire into short, identical lengths. (The exact length is what has to be determined by trial and error; it obviously depends on the diameter of the wire.) When you've made a dozen or so little pieces of wire that way, spread them out on a fireproof surface (you probably have a soldering pad of some sort) and hit them with a torch. In a few seconds the laws of physics will go to work; the brass will melt, and each length of wire will coagulate into a sphere. Drop the spheres into chemical blackener, let them dry, shoot them with clear flat lacquer, and you've got your cannonballs. Once you establish the initial measurement you can crank out a hundred of them in half an hour.
Chain plates are difficult. Each assembly has to be of a different length, due to the changing angles of the shrouds. In the early nineteenth century the chainplate assembly typically had four components: the iron strop around the deadeye, two long, open iron links (the descendents of the actual chain that was used for the purpose in earlier centuries, and the backing link, an iron loop that was forged into a dumbbell-like shape and spiked into the hull at both ends. The spike that went through the upper opening in the backing link also went through the lower end of the lower "chain" link, which was "pinched" together at that end to form an eye for the purpose. In a warship with lots of shrouds, the aftermost chainplate assembly in a gang had to be considerably longer than the foremost one. The discrepancy was taken up in two of the components: the backing link and the upper "chain" link. The lower links and the deadeye strops didn't vary. On a good set of plans or a photo of the real thing, the points where the links overlap, and the upper and lower spikes in the backing links, form straight lines.
On small scales like this, making all those individual pieces would be quite a challenge. The appearance of the finished product can, however, be pretty effectively faked by using one piece of wire, or even smooth-surfaced thread, and a simple jig. Drill holes in the channels for the deadeyes (or, if you really want to replicate prototype practice, cut notches for them in the edges of the channels and make a molding to close the notches and cover the edge). Mark two lines on the hull below, and parallel to, the channel, to establish the heights of the two rows of spikes in the backing links.
The jig consists of a strip of plastic sheet, about .020" thick and as wide as the opening in the upper link of the first chainplate assembly. Start by twisting or knotting the wire or thread around the deadeye and passing both ends through the first hole in the channel. Then make a half hitch in the wire or thread, at the point where the deadeye strop would hook into the upper "chain" link. Hold the plastic strip there, and make another half hitch in the thread or wire just below it. Drill the two holes in the hull for the backing link spikes. Shove both ends of the wire or thread into the upper hole. Make the backing link out of similar wire or thread. Make the spikes from brass or steel pins, paying close attention to the diameter of the heads. Shoving the pin into the hole on top of the wire or thread will hold the latter in place.
As you make your way aft, the jig will ensure that the "joints" between the "links" (i.e., the half-hitches in the wire or thread) are lined up right. When you're done, pull the plastic strip out and paint the whole business black. (If you used thread, try mixing a little Elmer's glue in with the paint.) You'll find it's difficult to tell that the "chain plates" aren't made up of individual links.
That's the trick I used on my models of the Bounty (1/110 scale) and the Hancock (1/128). I don't think I'd recommend it on any larger scale than that, but on smaller scales the illusion is pretty effective.
Disclaimer: this post has been edited. I initially typed it in a hurry, and realized later that I'd made some errors in it.