Without knowing where you are, I found my new iMac by callilng all the Apple Stores in my area every day until I found the one that I wanted.
I do have an advantage. There's at least 20 Apple Stores within a one hour drive from me. I found mine in one afternoon, set up exactly how I wanted. By the time I got there, the remaining 5 27" iMacs were walking out the door along with mine. This was better than waiting the 5 weeks that was the approximate time online.
I think you just have to be patient.