Most online stores deal with pre-built or custom built fixed wheels...
http://www.bikesnyc.com/catalog.php?...cat=Components
http://www.sheldonbrown.com/harris/fixed.html#wheels
http://fixedgear.americancyclery.com/

These are but a few out there. I was thinking about going that route as well but decided that I'd save my cash for a Surly fixed hub and some spokes and build it myself with an Open Pro rim I have already. Just seems that the saved cash always ends up going to groceries or my kids registration fees for soccer and the like.