Enter *Artist/Band name* Full Concert in search. But it's not a full proof method as most don't use those tags if they want to hide full concerts from the YouTube Police to keep them from being pulled. The search method will get you started, but you will have to dig deeper to find more concerts. The "hidden" stuff usually pops up at the end of the show, once the video has stopped playing and you get those thumbnails of more stuff of the same category.