Where can I buy a TFL William & Kate Oyster Card?

My friend has decided - months after they went on sale - that she'd like one of these as a novelty birthday present (I live in London, she doesn't, so isn't able to get one herself). They sold out of these limited edition ouster cards about 4 weeks ago in my local ticket office at Greenwich - does anyone know if any stations are still selling them, and if so which ones? I'd love to get her one but I'm not prepared to fork out the �20 people are asking for them on eBay..! x