I know that in the past SaberForge has customized the four 3W cree dies on their 12W LEDs to customer specifications, so I see no reason why they couldn't do a GGGB 12W for you if you requested it in your order notes.
Also keep in mind that SaberForge offers Blue and Royal Blue dies, and I'm not sure whether GGGB or GGGRb would be better for the specific shade you're looking for. Consult with them directly and give them an idea of what color blade you're looking for and they'll hook you up as best as they can