How to located a Corporate Store?

I have a problem that I've been told can not be handed at an authorized retailer.  I have been told that I HAVE to go in person to a corporate store to present paperwork.

However, when I go looking online to locate a corporate store, it is not clear which stores are corporate stores and which stores are authorized retailers.  I see some that are marked clearly as authorized retailers, I see others that are not marked as authorized retailers but I know for a fact that they are NOT Corporate stores.  I see some that are marked as authorized retailers but you can still make an appointment and others that say shop this store.

So, I actually called AT&T and asked them to direct me to a corporate store so that I could present the paperwork I need to present.  They gave me a store and address.  I went there, only to be sent away because there were NOT a corporate store!!!!

Come on this is hard enough as it is.  There has to be some way to search for corporate stores and not have to go through the entire list calling each store individually hoping that who ever answers the phone will actually know the answer.