Rivendell might still make the Atlantis and Rambouillet (or maybe just one of them) up to 68cm. I have a 64 in each, and I love 'em. They're getting expensive, though, up about $1000 since I got mine.
Just on the off chance, you might cruise thrift shops, like Salvation Army, occasionally. A 6'7" friend of mine bought a 27-inch (frame size, not wheels) bike the other day. It had been stripped and repainted, so we don't know the make, but it had older Campy components and a Brooks Pro saddle, forged dropouts and some other clues that it was decent quality. He paid $60 for it, I think.