i had such a business in the 2000s. mixed crushed bone powder from pigs with organic glue and a fine rock powder. used cad to model them like current skeletons, but a bit different, and bigger of course. milled the molds and casted them. we then put them into an old quarry to lay underground for a year, before we sold them to secret services in many countries. they obviously bribe scientists and deliver the fake skeletons to them at night. what an effort for nothing, but i didn't question it, i just wanted to make money. i also heard they now fake birds and insects.
Bulgaria