copper oracle
Legendaries are VERY random in how they spawn. You can ask in map/squad chat to try to get people to call them out and to kill them slowly (they die really fast) but sometimes you just have to camp their spawn area and not travel too far.
As for finding a map, just keep an eye on Central Tyria Squads in LFG. There is a RIBA squad there more often than not. And you can always make your own.
zealous token