Every area of Marleybone has some scrap iron. It mostly stays near boss hideouts, or central towers. It hides in corners, behind tanks and boxes, and near wooden chests. Your best bet is to choose your favorite area, mine happens to be Newgate Prison, and find the teleporters. Hop from Blue to Yellow to Green, searching all corners and nooks and crannies in the immediate area of the teleporter. When you've done all three - SWITCH REALMS! and repeat. It actually doesn't matter whether the realm is crowded, normal or perfect, the odds are good that you will find some scrap iron in one of the transporter areas. If you do this for about half an hour, you should come up with what you need.