As a freelancer it’s next to impossible, and it’s hard even when you work for any sort of publication.
There is no universal press pass that will get you through the door to everything, every PUBLICATION has to get a pass for every event 3 to 4 months in advance. The pass then later is handed to the dedicated photographer who is going to the event, who has to bring all the credentials with him to prove the validity. With so many freelancers and amateurs it’s only getting harder and harder to make room for yourself in a crowd of cameras and the presses are typically limited.