here's a couple of places at Shasta
Shasta Houseboat Sales (http://www.shastalake-houseboats.com/) also has boats on Oroville
Pearson's Marine (http://www.pearsonsmarine.com/)
As far as I know they are registered as boats but can be classified as a 2nd home with similar financing. When we were looking a couple of years ago, we were checking boat trader online, the Redding and Oroville newpapers, craigslist and a few other places. There were all kinds of used ones anywhere from about $3,000.00 (needed LOTS of work) on up to about $300,000.00.....lots of choices.