Even if they say they don't have any put your name on the reservation list, you may get it the same day. The day that AT&T announced their data plan change I called 5th Ave Store and they told me they had 64gb 3G and Wifi Models for sale. By the time I got down to the store they told me they had none. I put my name on the reservation list for a 64GB 3g and 32Gb 3G. Within an hour I received an email telling me the 64GB model was available. After two days I never received confirmation on the 32GB model, but when I changed it to a 64GB WiFi model, I received an email confirmation with an hour. Again, they had told me none where available but within an hour I had an iPad waiting for me.
I have seen hundreds of iPads sitting in the store room reserved for pick up. and each day some of the inventory becomes available because people are not picking up the units. Generally I think the 64GB units are easier to get. Apple makes more money by selling 64GB units and if people are willing to take what they can get, then why overstock on cheaper units. I hope this helps.
