http://rodcycle.com/
Check framesets, add $200 if one of their stock sizes don't fit, but I'm fairly sure their largest size is aimed at 6'5-6'6" folks.
I'm 6'8" and they put together an Adventurer for me that I've been beyond happy with.
Coupled with custom cranks from
HSCycle (they make Zinn's special sized cranks, but sell them for less) and I'm very happy.