Combine turkey broth and chicken bouillon in a slow cooker.
Place bacon in a skillet over medium heat; add garlic and black pepper. Cook and stir until bacon is crispy, about 10 minutes. Transfer to a paper towel-lined plate; blot to remove as much fat as possible.
Stir bacon mixture into the slow cooker. Add turkey, red onion, barley, rosemary, salt, and Italian seasoning.
Cook, stirring every half hour, on Low for 7 1/2 hours (or high for 3 1/2 hours). Stir okra and parsley into soup and continue cooking for 30 minutes more.
Cool soup to room temperature and refrigerate, 8 hours to overnight. Skim any solid fat off the top and heat soup on the stovetop.
If you use the turkey drippings, be sure to remove the fat from top of the soup after cooling in the fridge overnight. After skimming the fat, it is helpful to place a paper towel on top of the liquid to remove additional fat that you can't skim off. Discard the skimmed fat and the fat-saturated paper towels. Drain the broth from the bag or pan used to cook a turkey and place in a 6-quart slow cooker with 4 quarts water (or use 128 ounces chicken broth without adding water.)