I had the same problem and got one here:
(edit - link below assumes 31.8 clamp size - they have the smaller ones too):
http://www.universalcycles.com/shopping/product_details.php?id=12758&category=173
Or try the integrated stem/steerer, but it looks like they might not have the size you need.
http://www.universalcycles.com/shopping/product_details.php?id=17192&category=173
(edit - link below assumes 31.8 clamp size - they have the smaller ones too):
http://www.universalcycles.com/shopping/product_details.php?id=12758&category=173
Or try the integrated stem/steerer, but it looks like they might not have the size you need.
http://www.universalcycles.com/shopping/product_details.php?id=17192&category=173