Preheat oven to 350°.
Heat oil in a large Dutch oven over medium-high heat. Sprinkle lamb with salt and pepper. Place flour in a shallow dish. Dredge lamb in flour, turning to coat; shake off excess flour. Add 2 shanks to pan; cook for 2 1/2 minutes on each side or until browned. Remove from pan. Repeat procedure twice with remaining lamb shanks.
Add garlic to pan; sauté for 1 minute. Add orange juice, scraping pan to loosen browned bits. Stir in wine; bring to a boil. Cook 3 minutes. Stir in beef broth, thyme, and tomato paste; return to a boil. Remove from heat.
Add lamb to pan; cover and bake at 350° for 2 hours. Stir in rind and olives; bake an additional 30 minutes or until lamb is very tender. Place lamb on a platter; keep warm.
Place a large zip-top plastic bag inside a 4-cup glass measure. Pour cooking liquid into bag; let stand 10 minutes (fat will rise to the top). Seal bag; carefully snip off 1 bottom corner of bag. Drain cooking liquid and olives into pan, stopping before fat layer reaches opening; discard fat. Bring cooking liquid to a boil over medium-high heat; cook until reduced to 2 cups (about 20 minutes).