I was listening to a SW podcast recently (it may have been Imperial Holonet Radio, can't remember for sure), but they mentioned that one of their forum members that works at Target said that this is an online only exclusive, and that is why you aren't seeing them at retail. Take that with a huge grain of salt, because obviously it is a "friend of a friend who knows a guy" type of scenario - and, I don't think we've ever heard anything like that before.
That said, I thought these were supposed to show up once the UBP inventory got pushed through the system. The UBPs have been long gone for awhile at our local stores, and I've never seen a Rancor there. I ordered one online back when they were available at Target.com (not sure if they still are?), and I'm glad I did. Hopefully they'll make it to retail as well though, it really is a nice toy.