Send an e-mail to them ? Do a whois to get it.
It's WhoisGuard'ed, so no help there.
You'll probably just have to see if they'll respond to an email.
The e-mail adress provided by the WhoisGuard is linked to their real e-mail address. Send an e-mail adress there and ask nicely who's owning the domain, and they might answer, or they might not.