I have a feed supplier that runs a custom mix for me, however you can achieve a very similar result with common items from the hog and horse sections of the feed stores.
Wheat gem Oil as a top dress-Takes a few weeks to get through to the feather but also adds a nice layer of heavy fat to the body.
Cod Liver Oil as a top dress
Fat supplements such as Fat and Fluffy or Sumo mixed into the feed
Black oil sunflower seeds in diet
Floating Fish food in diet
High fat dog food in Diet
Show Hog rations with Fat content not less than 5%
Redcell a liquid vitamin supplement often used as a top dress
B12 liquid in water to keep them active and lively in the coop
My mix consists of twice cracked popcorn, oats, wheat, barley, black oil sunflower seed, fish meal, floating fish food, calf manna, 22% protein 7.5% fat hog pellet, 10 gallons molasses, 10 gallons wheat germ oil, 10 gallons soy oil. That is for 1000lb