You can find it on Amazon. But personally, I just go with Ghirardelli bittersweet chocolate when making my breakfast stout inspired beer. It's chocolate going into a dark roasted beer. I wouldn't get too set on buying expensive chocolate that you won't notice a difference with.
Also, I recommend using the chocolate bars as opposed to the morsels. The morsels do not melt down as well in the kettle. If you break the bars up into quarter-sized pieces, they will melt perfectly in the beer.