You should be able to find a decent selection at any good bike shop. The new interest in 29" wheeled mountain bikes means suppliers such as Trek stock 700c disc specific wheels. Quality Bicycle Products, a wholesaler for bikeshops, stocks 700c disc wheelsets which the shop should be able to order for you no problem.
A good bicycle shop should be able to build you the wheel you are after. If you choose to build the wheel up from scratch, you can pick either a road rim like a Mavic Open Pro, a Salsa Delgato X (cylcocross rim) or Bontrager Disc Specific asymetrical rim to build on whatever disc hub you'd like, such as Shimano, Surly, Hugi, Chris King, etc...
Are you looking for a superlight race wheel or a durable all-season training wheel or what? Please describe and I can help out =]