Luna was out for about a month before Hot Topic decided to start getting rid of all of the pony vinyl figures. Seriously. I've been to all of the Hot Topic's in my area within the last few weeks and none of them have the vinyls outside of blue Discord. Other people have been saying pretty much the same thing... for once, I'm glad I pre-ordered, because finding her is impossible.
So yes, she was out in December and part of January, but disappeared soon after.
You could probably find Twilight at Barnes & Noble. I see her there a lot along with Big Mac.