haha come on... really you guys?
Listen, there's nobody outside of the major organizations that would stand a chance against top-tier opponents, end of story. I mean seriously, do you understand the level a guy like GSP is at?
GSP could walk into most any jiujitsu school and decisively dominate the head instructor. Then he could walk into most kickboxing schools and beat up the instructor there too. You need strong competition and paid sponsors to be able to train full time, at your hardest and best at the best gyms - there's simply no other way.
I don't get the concept really. If there was a dojo out there that had a fighter or was training fighters who were better than the fighters at say, Black House or GregJackson's camps... wouldn't fighters train there instead? No such place exists - there's no underground karate dojo or something that has fighters better than MMA's top fighters.
Look at Junior Dos Santos for example. He's the Brazillian HW Kickboxing champion, 18-0. He's still slowly climbing the ranks in MMA.
Demian Maia is easily in the top 10 in the world in terms of pure grappling skills. Still climbing the stacked MW ladder.
Unknown underground fighters who could beat top tier fighters simply do not exist. Sure there's guys who have insane natural talent and are maybe slowly working their way up - Jon Jones comes to mind (even tho I'm not a fan). But it's not like these guys could just come out of the woodwork and beat Shogun, GSP, Penn, Fedor, etc.