BUG: gunslinger class not showing up in classes.

I can only get to it by clicking on this link. not from the dropdown menu. 

Are you talking about your character sheet or on fighter class page?

fighter class page.

I'm not sure why the page is so hard to get to and not listed as an unofficial subclass on the fighter's page the same way UA brute is. It is a question only the Devs (and maybe mods) know the answer to.

Quote from DxJxC >>

I'm not sure why the page is so hard to get to and not listed as an unofficial subclass on the fighter's page the same way UA brute is. It is a question only the Devs (and maybe mods) know the answer to.

 
It's been discussed before and their answer is that it is 3rd party and having it on the Fighter page might make it seem official when it isn't and this might upset WotC. It was suggested they could include a banner or something to indicate it's status as third party and not official but they ignored this. There is talk of a menu redesign that may be able to simplify this but this is not a priority at the moment.

TL;DR Not a bug, it is by design.

The Fighter forum has a pinned thread with a link to the page that has the Gunslinger subclass details.