The scoring information can probably be inferred from the original article: Durso LE, Latner JD (2008) Understanding self-directed stigma: Development of the Weight Bias Internalization Scale. Obesity, 16: S80–S6
If that doesn't work out, I suggest contacting one of the authors. Laura Durso is at something called the Center for American Progress in Washington DC. Janet Latner is at the University of Hawaii, in the Department of Psychology. My guess is that she will be easier to get in touch with.