Not sure if this will help anyone but its a good way of getting a legendary weapon. A good one and one you'll actually want to keep and use.

Head over to Old North Church and make a save just outside the door. Go in and find the legendary ghoul, he'll either be the one immediately to your right as you enter the church or one further down in the middle of the pews. Kill him and see what legendary item he drops, if its not something you want then reload the save from outside the church and try again.

If he does drop something you want but the bonus isn't what you need (say you want a 2 shot .44 pistol and he drops a neverending .44 pistol for example) just reload the autosave the game makes when you enter the church and try again.

If you load the save from outside the church it will spawn a new ghoul with a new legendary item, if you load the autosave from inside the church it will spawn the same legendary item but with a different bonus.

Another good place to do this is the basemant in Croup Manor. You want somewhere where you can enter into a new map and find a legendary creature straight away so you save time on hunting for one only to reload if it doesn't drop what you need.

The pain of doing that might be fine for console users, but PC users can use mods to craft legendary items.

There's a rumor that if you find a Glowing One near a Legendary ghoul, you can farm the crap out of it by killing the legendary while kiting the Glowing One. Loot the dead ghoul, then bring the Glowing One within range of the corpse. He'll resurrect the dead ghoul, and you can kill it again for another drop.

I have yet to come across this beautiful little setup, but I'm hungry to try.

It'll probably be the identical drop. Since using the console to resurrect the dead Legendary usually does not spawn a new weapon in its inventory, I'm guessing that if the Glowing One resurrects the Legendary it'll spawn without a weapon too, but hopefully I'm wrong.

I find at least there must be one Legendary Gunner in the Gunners Plaza.

Last time I met 3 legendary gunners there. I forgot for what purpose though. And I got decent caps from selling the loots purely from there.

I wish bethesda made an extra slot in weapons crafting for legendary components or somethingthe like enchanting in skyrim.

There's a mod for that.