They can usually be found at the top of the page, but are also sometimes placed at the very bottom.
Here are a few examples of the designs for these links;
The Kooks 
The Fray 
The Levellers 
The Wombats
All of these are very dark, with the buttons in a white colour. On The Fray's website it also has a link to a cart, this is there so people can buy the music direct from the website.