Generally speaking, there's a long list of gatekeepers -- about 20 gatekeepers for every AI that wants to play. Your best option is to post "I'm a gatekeeper. Please play me" in every AI box thread, and hope that someone will message you back. You may have to wait months for this, assuming you get a reply. If you're willing to offer a monetary incentive, your chances might be improved.
Update 2013-09-05.
I have since played two more AI box experiments after this one, winning both.
Update 2013-12-30:
I have lost two more AI box experiments, and won two more. Current Record is 3 Wins, 3 Losses.