I looked it up, apparently we haven't seen Luna yet.
The stuff from wiki is a little contradictory. She's either across the eastern sea or on the eastern sea. Across would be a problem, I don't see how clark wll cross the atlantic in a timely manner.
"In my book, there's a map. Chart a course to the Eastern Sea. There's a clan there, led by a woman called Luna, a friend. Tell her I sent you. "
- Lincoln to Clarke
Luna is a character mentioned in The 100. She is the leader of the clan east of the sea, and then across it. Lincoln explains that Luna will allow the Delinquents to stay with them. Eventually, Lincoln attempts to take Octavia to Luna and her clan but they never make it there.
In I Am Become Death, Lincoln tells Octavia of a clan that might take them in.
In We Are Grounders (Part 1), Lincoln tells Finn and Clarke to take everyone and flee to Luna's tribe.
In The 48, Lincoln is teaching Octavia Trigedasleng to help her fit in when they get to the sea. They end up never making it.
In Wanheda (Part 1), Octavia suggests to Lincoln they leave Arkadia and go to Luna's clan. He tells her Luna is in hiding for a reason and won't take them.
In Stealing Fire, it is revealed that Luna is a Nightblood and the eighth officiate who was the only other survivor of Lexa's conclave.