Thanks for the hint. I found it at last. It's been way too long since I played Fallout games, and forgot how to search for things. But I got another problem. The quest for restoring trading between Miners and Farmers seems to be bugged for me. As I talk to the owner of the mine, I got only one dialog option: "Have you told Farmers my terms?" And that doesn't make sense at all, as I have no idea what his terms are?