I hate to be the bearer of bad news BN, but apart from arranged 'meet and greet' arrangements, no band will issue back stage passes to fans.
As a music journalist, I have been backstage to hundreds of gigs, but by the time the band get to stadium level, as the AM's now are, security is so tight that even bona fide journalists get escorted to the band to do an interview, and then get escorted back to the public area - hanging around in the backstage area is simply not permitted.
So, unless there is a pre-arranged 'meet and greet' which is usually advertised, I am afraid there is no chance of getting back stage, sorry.