I went looking for the official magazine featured in this post and followed the link to Titan magazines
I then got quite confused, because there are two 'order now' links from this page. If you follow the smaller top one, it tells you that the Serenity mag has sold out and cannot be backordered. If you follow the bigger order link, it takes you to an ordering page!
So I called the company to check. The woman said they had copies in stock, so it was fine. I told her about the website problem, and she said she'd check it out. I think it's just that the smaller button is misleadingly labelled, as it's really about ordering back issues which obviously don't exist for Serenity.
So, UK Browncoats, all is not lost. It's 5.70 pounds, including shipping costs. I've ordered mine.
The USA & Canadian versions of the website do say that all copies are sold out, so no luck there. Strangely, the Australasian version of the site just seems to mirror the UK version, with prices in pounds!