Several sources list Saaz as a potential substitute, but I don't buy that. Tropical fruit (passionfruit, kiwi) and grapefruit would lead me to think some of the 'C' hops along with El Dorado, Azacca, or Meridian might get you in the ballpark. There may be some of the newer hops out there now which would be a better single hop sub, but I am not currently familiar with them.