theres loads on ebay
http://www.ebay.co.uk/itm/3x-ATMEGA328P-PU-Arduino-UNO-R3-Bootloader-ATMEGA328-P-PU-Pico-power-Micro-/221153175158?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item337dc1a676
you can buy 1 2 3 or 6 or 10 units i dont know where you are so use your nearest supplier