You can find some decent ones - quarter sized - along the beach and shallow water at Venice. The best time is after a storm or beach renourishment. As for diving there are a series of reefs offshore that are an easy swim. The relief is only about 2 ft. We look for the "debris fields" inside the reef. We usually pick up around 300 teeth and several good sized prehistoric bones, vertebrea, etc. If you're at the main beach - with the bath house at the end of Venice Blvd, go just south of the bath house where the pipe goes into the water. Surface swim to the "No Wake" bouy and then hit the bottom. Using your compass swim due West until you hit the "cement block" artifical reef. Then swim due West another 50 - 100 yards until you hit the black rock. Look in the washout areas for the big teeth. Visibility this time of year is dropping quickly due to the rainy season - now just a foot or two unless your lucky.
Beach combing for sharks teeth is good all the way south to Little Gaspirilla Island.
As for the Peace River you need to look in the bends of the river in the gravel piles. Take a sifter if you can and go into knee deep water. Shovel out what you can and sift through it. A lot of areas near the parks and public access points are pretty well picked over. If you have a canoe or kayak go up river to the remote areas. The best times are after rainy season when the new stuff is washed down.