They did a pre-release for one of the four, and some of those have gone up on Yahoo!Japan already. The pre-release includes a special "I Love Mew" bag. Apparently, these pre-released plushies can only be obtained by winning them from a claw machine.
I can't wait for the official release! They all look adorable. Who else is excited? Also, is there anyone out there who would be in Japan and have access to these plushies when they come out in January? I'm hoping to find a middleman when the time comes. Below, I've included the links where I found my information from.