Where can I find LEGO minifigure sunglasses in black and a rock band guitar for the new Doctor Who set? I have searched on ebay and LEGO.com.
For guitars, this search shows what BrickLink has available. As an example:
Note that BrickLink is a marketplace - they give you access to thousands of individual sellers with their own stores. You might want to find a seller who has both items you like in stock, so you can purchase and only pay 1 shipping/handling fee.