Who do you bring the fingers to in fallout 3?

There are a group called the regualtors, they are near wheaton armory (i think) on the right side of the map, about half way up. its a little north of wheaton

Once you get the lawbringer perk, which makes the fingers appear on dead bad guys, there should be a map marker added that you can discover and then fast travel there in future.

You are looking for a shack with a few brahmin outside. There is a woman called Sonora Cruz inside. She buys them from you and gives you a cool looking jacket when you join them.