Most large automotive retailers, including O'Reilly's, Advance Auto Parts and Auto Zone, carry window motor parts and accessories. The availability of the parts largely depends on the make and model of the vehicle.
Window motors are also available for purchase online through retailers such as Amazon.com, JC Whitney and Walmart, as of 2015. Auction sites like eBay often list new and used parts for window motors as well. One potentially cheaper way to get parts is to call a local salvage yard, especially if the vehicle is common. This can mean putting in time to call and pick the part, but the savings can make the time investment worth the hassle.