Take a look at the newest VeloNews buyers guide. It lists out the reputable framebuilding classes:

Bamboo Bike Studio, Brooklyn.
R+E cycles, Seattle.
Bohm, Tuscon.
Fattic, Michigan.
Flanigan, Massachusetts.
Brew, North Carolina.
Sanner, Austin. (although we are not running classes right now).
Hot Tubes, Massachusetts.
UBI, Ashland OR.
Yamaguchi, Colorado.