A couple of books I've ordered are on '4-6 weeks' availability. They have been since I ordered them on the 25th of June. One book out of that order made it to me in early September; the other two now have projected dates of between mid-October and late November.
I'm leaving the order intact, because I'm in no hurry, but I've had this problem before: they just don't know when to give up and tell you that actually they can't get hold of it.