Combine rice with broth and 2 cups of water in a large saucepan and set over high. Bring to a boil, then reduce heat to low. Simmer, covered, until liquid is absorbed, about 30 min.
Grate unpeeled tomatoes using a box grater into a large bowl. As you get close to the stem, the peel will be easily removed. Discard peel. Pour tomato pulp into a strainer and drain. Discard juices. Set aside.
Season scallops with 1/2 tsp salt and pepper. Melt 2 tbsp butter in a large, deep non-stick frying pan over mediumhigh. Add scallops. Cook until dark golden, about 2 min per side. Transfer to a plate and cover with a piece of foil to keep warm.
Add remaining butter to pan along with flour. Whisk to mix. Cook until mixture smells nutty, about 1 min. Add clam juice, then scrape up brown bits from pan bottom. Stir in garlic, celery, onion, pepper, tomatoes, thyme, bay and remaining salt. When mixture starts to boil, reduce heat to medium. Gently boil, covered, 10 to 12 min. Remove thyme sprigs and bay leaves. Stir in Tabasco and parsley. Scoop sauce into 6 dishes, then top with rice. Lay 2 scallops overtop.