I think the real question is ...
Why would you even want
@Rick Schwartz to buy one of your domains?
Don't get me wrong .. this has absolutely nothing to do with him personally .. I don't know him at all aside from his reputation of selling domains at amazing prices.
But in the end .. he's a domainer like the rest of us here. I can't be 100% sure .. but I think it's safe to say he got to where he is today by buying domains for low prices and flipped them at high prices. As such he very likely won't be paying/offering anything close to end user amounts.
If you're looking to liquidate "Schwartz quality level" domains .. then you'd likely do better at NameJet or Sedo's Great monthly auctions or another reseller focused auction platform where even if it's all domainers, at least you'll have a bunch competing against each other pushing the prices up a bit more than if you approached a single domainer.
That being said .. if you really do want to contact him .. I'm going on a limb here .. but maybe try the contact form on his website? lol
http://www.domainking.com/contact.php