While I can't answer about stock quantities, I can give you a piece of advice.
I'm going to be going to the store to get an iPhone since orders are about 4 weeks off. My plan is to ring my local store just before the close of service on Sunday, to check how the stock levels are before going on Monday. Obivously your situation won't be the same, but ringing ahead to check stock levels and then going down early the next day is a good bet I think.