According to their FAQ, there are few requirements to be eligible to attend the Second Amendment Blogbash. For example, you don't have to be a blogger, only a "new media publisher." You don't have to focus on gun rights, either. You only need to support the Second Amendment. The blogbash is at the NRA convention, but you don't have to be a member of the NRA, either.
But there is one big anti-requirement: if you write for the Examiners, you are not allowed.
I have never been a regular reader of either of the two big "gun" bloggers involved, because I recognized them quite quickly as cliqueish NRA apologists. A lot of other bloggers think they're great. I don't. If you do, you need to read the previous link and decide if you really want to associate with--or even blogroll--people who practice such unjustified exclusion.