McNally only drops the Hammer Buster. The only way to get the Lady Fist in the game is as a reward from the Uncle Teddy mission and you can only get it once per playthrough. The only way you can get it multiple times in a single playthrough is through trading with other players. There is a way of farming for perfect prefixes, parts and elements, though. Once you complete the mission, don’t turn it in. Save the game first by passing a save point and then turn it in, but don’t accept the reward immediately. Instead, just take a look at it and check if it has the prefix, element and parts that you want. If it doesn’t, dashboard out of the game. That means a force-quit without saving. Once you reload the game, you’ll still have the mission completed and you can turn it in again. Repeat this process over and over until you get the Lady Fist you want.