If you can't find buyers, donate them to the science dept at a local school.......says the marine science teacher with a classroom full of coral skeletons......lol
I go to an annual craft/gift fair every year and there’s a booth selling coral skeletons every year. The smallest skeletons sell for around $90 and some of the larger ones sell for a few hundred dollars. So you might want to look into what it costs to rent a booth at something like that.