I dont know if anybody found this one yet but ill post just in case. I was doing the daily and i found it by accident. First mission from how. After you defeat the walker, and you get to the platform that forces you to leave your pike behind. I was trying to get my pike over and i got inside a small cave in the left side of the platform. Trying to get my pike out, i noticed the coin on the ground. I am a noob at posting pics on here. But if someone can do that will be cool thanks.