If you found one it wouldn't be too hard to add some marine-kit parts to make a powered ferry, like the Solano or the Ramon.
Here's the Ramon, which plied Suisun Bay along with the Solano. The difference is that the Ramon worked for the Sacramento Northern, an electric interurban, rather than a steam railroad.
I doubt they make a model of this one but here is the S.S. Badger that went across Lake Michigan for the Pere Marquette and later the C&O. Now it is strictly a carferry which is still pretty cool!
I looked at the site, Ralph. The barge shown as a car float is some sort of floating passenger station. I can't imagine it being of much use to an American prototype modeler, but the plain barge shown next to it could easily be kit bashed into a car float.
I don't know if you had a chance to read the description of the car float. I hadn't when I first posted the link...but after I did I see its out of production!!!!!
I didn't really look at the description when I posted before so I didn't see that it was out of production. It just didn't look like something that could be used for American prototype. The standard barge is still available and looks like it could be used if someone didn't want to scratch build. I looked at your model, and I would scratch build. I like your model!
One of the Kalmbach trackplan books has an article on Cubicle railroads which includes one with a carferry. There are elevations and plans (though they are fairly small), but they acn be scaled up with a photocopier - I have a set of them for HO somewhere
Shortliner(Jack)away up here in the Highlands