I have a couple new Ipads and can't login while at work.

We purchased a few ipads for work but can't set them up while at the office. Something in our firewall is stopping them from connecting to the Apple servers. IT has looked everywhere and can't find any server being blocked that would be Apple but can't find a list of Apple servers to "allow". In addition we have it setup so that nothing out of country can be connected to, are Apples servers in the US?