Prepare the Ossobuco. Tie the rosemary, thyme, bay leaves, and cloves together securely in a 4-inch square of cheesecloth. With a vegetable peeler, remove the zest (yellow part of the peel only) from the lemon in wide strips. Do the same to the orange. Squeeze the juice from the orange and reserve separately.
In a wide, heavy nonreactive casserole large enough to hold the veal shanks, heat 2 tablespoons of the olive oil over medium heat. Add the onions and cook, stirring occasionally, until wilted, about 4 minutes. Add the carrots, celery, and the cheesecloth bundle of herbs. Season lightly with salt. Reduce the heat to low and cook, stirring occasionally, for about 10 minutes.
Meanwhile, pat the pork shanks dry with paper towels. Tie a piece of kitchen twine securely around the perimeter of each piece of shank to hold them together during cooking. Season with salt and pepper and coat with the flour, shaking off any excess. Divide the vegetable oil between two large, heavy skillets and heat over medium heat. Add the shanks to the skillets and cook, turning once, until well browned on both sides. (Alternatively, the shanks can be browned in batches in a single skillet.)
Add the browned Ossobuco to the casserole with the vegetables. Add the tomato paste, stir it into the vegetables, and cook, stirring occasionally and turning the shanks once or twice, for 10 minutes. Add the wine and bring to a boil, then add the reserved orange juice, the carrot juice, celery juice, and the orange and lemon zest. Bring to a vigorous boil over high heat and boil for 10 minutes. Add the crushed tomatoes, reduce the heat to low, and simmer, covered, for 30 minutes.
Stir in 1 cup of stock. Cover and simmer over low heat, adding stock to keep the level of liquid in the casserole the same, until the shanks are tender, about 1 ½ hours longer. Rotate the pork shanks in the casserole as they cook.
Meanwhile, prepare the barley and the gremolata (recipes follow). In a large saucepan, bring the water, carrots, onions, celery, bay leaves, and olive oil to a boil. Stir in the barley and cook until tender but still firm, about 20 minutes. Drain the barley and set aside. To make the gremolata, toss the lemon zest, parsley, and garlic together in a small bowl until blended and set aside.
When the veal is tender, remove it from the casserole and cut off the strings. Pass the cooking liquid through a sieve, pressing hard on the solids to remove as much liquid as possible. Return the meat and sauce to the casserole and bring to a boil. Check the seasoning and keep the veal warm over low heat.
To finish the barley, heat the butter in a large, heavy skillet over medium-low heat. Add the barley and cook, stirring often, until it is heated through and coated with butter. Season with salt and pepper.
Serve some barley and two pieces of the veal on each plate, sprinkling the veal with the gremolata.