If you consider building a model of a paddlewheel steamboat, think of doing a lot by yourself. There are only very few steamboat model kits around, the most accurate but also the most expensive one being the SAITO model kit of the Delta Queen.
But if you’re an somewhat experienced model builder, look for model plns from John Fryant and Alan Bates. Unfortunately they’re hard to find in these days; maybe you’re lucky at eBay.
To build an authentic steamboat model, plan to spend a lot of time in research before you even think of starting the build process itself. Find pictures of the boat you’re thinking of. Check plans and books for specific features of the boat and find out what colors most likely had been used for this boat. Take in account that the boats did change their appearance all the time, so you also will have to make a decision about the time period from which you’re building your model. We highly recommend to find a copy of Alan Bates’ Western River Steamboat Cyclopoedium which is the most comprehensive resource of information about every piece and part of a steamboat, especially written for model builders. If you’re lucky, you’ll find a copy at eBay.
When you’re finished with your model, you’ll find out that you became a steamboat expert and know everything about your specific boat.
If you’re not passionate enough to spend hundereds if not thousands of hours for a well sized model, probably even remote controllable, consider a plastic or paper model. You can improve these models, too, to be more authentic. It just doesn’t cost as much time as a “real” model boat.
We do have a website (sorry, only in German language) with long lists of model building resources specifically for steamboat and paddlewheeler models. Including sources for model kits, plastic models, paper models, model plans and books: www.steamboats.de