Ask HN: Can I volunteer my site for black box pen-testing?

Is there a platform/matchmaking site where people who want to hone their pwning skills offer free pen-testing services, and people who want to battle-test their (private) servers offer those up in turn?

Of course there would need to be some contractual assurances given on both sides, plus maybe some kind of reputation system...

Just thinking aloud, or does this maybe exist already?