Where can I find LEGO Doctor Who sunglasses and guitar?
Check out BrickLink. They have a whole range of Minifig heads with sunglasses - pick the one you like. 



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.