There are a large number of extra models you can get; Elven Cavalry, bat swarms, Smaug the Golden, more Dwarves, etc... The only scenario in the book is the Battle of Five Armies, but there are rules for making your own scenarios as well. And as for purchassing it, if you don't have it already I don't think you're likely to ever get it; as far as I know it's sold out worldwide (since there were only 8000 or so made).