Get some plaster of paris and make a plaster mold. Let it dry/cure thoroughly and then spray it with several coats of clear lacquer. Find a plastic form....a good one to use is the deep half of a clam pack of some sort. Use some super glue to glue your plastics down on the bottom inside of the form and then fill it with the plaster of paris when its mixed and let it set a couple days. Then trim the plastic form off and remove the plastic baits and let the mold dry completely for a few days and treat with the spray.