You could try downloading a mod that changes the rarity and chance of legendary encounters, open with FO4Edit/CreationKit. FO4Edit: When you open the program it will give you a list of your ESPs, scroll down to the one from the mod you downloaded and right click to deselect all and then select the esp you want. After it gives you a message saying it finished loading on the right side of the screen click on the "+" that is located to the left of the mods name and look for "fDiffMultLegendaryRarity"(The rarity of a legendary enemy) and "fDiffMultLegendaryChance"(Chance of a legendary enemy spawning) and modify then to your hearts content. EDIT: There are different options for the difficulty you are playing. "fDiffMultLegendaryChance_TSV" = Survival.
