[Naydef]

Originally Posted by Tim q Where can i find it to download?

It's better to generate one, most maps don't come with NAV file.
Just type nav_generate on the chosen map and wait for the process. Generally you don't want to do that manually for every map.

There is an auto nav generator plugin, however I remember it was unreliable and would generate nav files every time.
There's a user who modified the plugin for TF2, give it a try.