Lots of places. Rock Auto, Auto Zone, Amazon, Brake Performance, any parts store that deals with Centric, Wagner. Do some homework, and pick your vendor.
watch out for centric rotors tho, got a defected one from partstrain.com, supplier of centric. holes dont match up due to shity bolt pattern drilling. Good thing tho their sending a replacement one and price is cheap for them but they rape you on shipping.