The best place to look is straight from the source: contact Steinway in New York. If you're okay with not buying something brand new, a good idea might be to check out the piano sales at Aspen after the festival. All of the concert instruments used in performances are sold off afterwards. This way you know where they've been, how they've been played, and, if you went to the festival, you would also have the opportunity to hear what they sounded like as a listener instead of a player ...
You're lucky -- I'm jealous!