Where do you get backstage passes for pink?

It basically comes down to: "know somebody." Backstage passes are normally not for sale. The band or artist (generally through their manager or producer) is usually allowed to have pretty much anyone they want backstage, so if you know a member of the band or their road crew that would be one way... though if you know a member of the band or road crew, you probably wouldn't even be asking the question. Also, it's fairly common for the promoter of the concert to have a limited number of passes which are usually given out to, well, promote the concert (as a prize in a radio station contest, for example).
Finally, the owner of the venue (the concert hall, arena, stadium or whatever) will almost certainly have a house manager present, along with security staff and potentially other crew members (stagehands or technical crew. though often these will be present for setup and strike only and not necessarily when the performers are there).