I would avoid bread mold when making blue cheese. Bread mold can contain a variety of fungi including Aspergillus, Monascus, Rhizopus, Penicillium, Fusarium and Monascus. Each of these species has its own color. The Rhizopus is black and fuzzy, while the Aspergillus is finer in texture. The Penicillium species is more grayish-green, has a white border to it and is fuzzy in appearance.
Get some P. roqueforti from a cheese supply shop and use this.