Is there a Spell or Magic Item that will extend the range of racial Darkvision?


My group has decided to head down into the Underdark. And I would like to optimize my Half-Elven Darkvision (60′)

Assume I have access to any spell or magic item that is in one of the hardcover books.. and do not want to use UA or 3rd party.

What is the maximum Darkvision range I can get?

Note: I would prefer to avoid Polymorph if I can.