Also, available are beaks which are outside corners. They are used as an outside corner for a shower wall or backspash. 

In this listing is also an AU that is available. These are used for the corners for bottom-set sinks. You can buy the matching quarter-round and 4 AUs (corners) in one purchase from this listing. Simply use the drop down menu to order however many quantities of quarter-round, AUs, or Beaks. 

If you have any questions, feel free to reach out. I am happy to assist.