To make chicken stock, place all ingredients into 8-quart stockpot. Bring to a boil. Reduce heat and simmer for 30 minutes, skimming impurities off the top. Remove chicken pieces. Allow chicken to cool, remove meat from bones, and then return bones to stock. Reserve chicken meat for the gumbo. Continue to simmer stock for additional 2 1/2 hours.
To make gumbo, begin by heating oil in a large pot (preferably an enameled cast iron or other heavy-bottomed pot) and cooking garlic, onions, peppers, and celery until soft and translucent. Add sausage, tomatoes, tomato paste, and stock. Bring to boil, reduce to simmer and add okra and reserved cooked chicken meat. Season with hot pepper sauce, cayenne, salt, pepper, and file. Simmer for 1 hour until flavors meld together. Stir in chopped parsley. Serve over hot rice and garnish with julienned scallions.