I just went and collected some and you can pick them now, my personal experience is they don't occur north of Rockport with much frequency, you may find an odd mangrove now and again further north but I can't say for sure about Galveston, they like marsh land, they grow in really foul mud and aren't much on freezes. Port Aransas, Mustang Island and North Padre Island seem to be the best sources. You may find some near Galveston but they don't like groomed beaches and sea wall areas, look in the marshes near the coast on the bay side. I just got back with them so we still need to clean, sort and pack them but I can get one to you if you prefer. The farthest north I have personally seen them is where the Guadalupe river enters the Gulf of Mexico near Victoria. That marsh delta is actually really thick with them but is a protected nature sanctuary but you can see them from the road in huge groves.