After quite a bit of badgering by yours truly, the good folks at TT have started production of the new 44mm headtube stock. As of May 12th, I have a bit of extra stock still left after preorders have been filled, the tubing will remain available until it is gone.
For technical details, refer to the MTBR thread here.
As of fall 2010, I am out of stock of this tubing. It will be available directly from True Temper, or through Henry James in smaller quantities - contact them for details. Paragon Machine works is also producing a very nice 44mm ID head tube in a variety of lengths.