In the Bahamas, the shells are quite plentiful. There are a number of Conch Fritter restaurants. I am not sure they are sustainably harvested. I tested out a number of shells that were already made into a horn in Freeport on the Grand Bahama, but they were very crudely made and rather expensive, so I purchased one for five dollars that had been harvested for food, then plugged the hole where they cut the animal out of it. There were also shells in Nassau on Paradise Island. I seem to remember seeing a native selling a bunch on the dock. The Bahamas are fairly sparsely populated, and there are many small islands/Cays with no inhabitants, so I would like to think the Conch may be OK there. In general the shells are byproducts and people eating them are the problem.