There are occasionally domestic 1st class seats on ebay and some custom refurb places (www.motoart.com). Other than that, I'd imagine that a random used Y class seat would be more useful as a conversation starter than an actual piece of furniture.
I'm wondering when the current crop of internation business and 1st class seats will start showing up for sale. For as much as we complain about airline seats, those things are just as comfortable as your average lazyboy ... i'd love to snag one!
and others re-confirguring their biz class sections with the new lie-flat "shell" seats, I wonder if the time is right to get some of the older intl. biz/first class ones on the cheap!