Bill, that fender really is a good grab! I know how hard they are to get as I would love to snag one as well for my CB77. Right now I have an aluminum shell on my stays and brace, which actually turns out to be pretty close to the original. Its painted the silver colour, but the soft aluminum and the one-time closesness to oversize tires I once ran, caused it to get dimpled and dented from stones it picked up. I'd rather have a harder original steel shell.
BTW the stays on these fenders are often still in good shape (just the fender shell itself gets damaged or chopped), so I've found them easy to re-attach to another shell. My CB77 is an early one so that the centre brace would be different than the one you got, but it probably could be replaced with another. I've actually seen guys use the CB160 fender on these models, although they have to modify the mounting as this model's fender has totally different stays to hold it. Those CB160 fenders are much easier and cheaper to snag.
So, if you know of a cheap steel shell for the CB77...I'd love to hear, as I have the stays and centre brace.