"Valkyrie" Sigrdrifa is a limited edition with unique style 30 Fullsets Limited, the basic doll(without make-up) will still be available. More detail: RingDoll
I think they can after a while! I doubt they’ve listed her head yet, but when they do you’ll just have to go directly through their website to their head section and find her number. It’s a little difficult to find since they aren’t listed by name, though.