Here are a few of the references I'll definitely be consulting for my ethnography:
Spencer, Amy. 2005. DIY: The Rise of Lo-fi Culture. New York: Marion Boyars.
Although this book doesn't directly pertain to wizard rock, I'm hoping that this source will give me a better understanding of the DIY culture that is central to wizard rock.
Kidd, Dustin. 2007. "Harry Potter and the Functions of Popular Culture." The Journal of Popular Culture 40(1):69-89.
This article discusses why Harry Potter fans create a community based on popular culture, the same community that produces wizard rock.
The Wizrocklopedia (anonymous staff member). n.d. "The History of Wizard Rock." http://wizrocklopedia.com/index.php/the-history-of-wizard-rock/
This article from a wizard rock fansite provides a comprehensive history of the genre and some insights from an anonymous scene member as to what the scene "stands for" and accomplishes.
I've also found plenty of fansites, Myspace pages, and mainstream media articles about wizard rock that will give me lots of material to draw from.