Poachers kill elephants for tusks and rhinos for horns because these can be sold for a high price on the black market. The killing has occurred both in the wild and in zoos, and thieves have broken into nature museums to steal rhino horns from exhibits. Sometimes news reports describe how police crush or burn seized illegal ivory, which seems counterproductive, because it reduces supply and thus drives up the price. A higher price increases future poaching. Perhaps the police are in the pay of some illegal ivory dealers and are deliberately helping drive up the price by destroying competing dealers’ products.
Instead, the price of ivory and rhino horn should be reduced so that poaching becomes unprofitable. Many organs have been grown in the lab using a collagen scaffold seeded with stem cells from the appropriate tissue (bladder, skin, heart). Growing elephant tusks or rhino horns in the lab should be feasible using similar techniques. Flooding the market with cheap lab-grown horns and tusks would eliminate the incentive to poach.
The demand for ivory and rhino horn is mostly due to silly beliefs about their medicinal properties, so the buyers may not want lab-grown substitutes, believing these to be ineffectual (which these are, just like wild-type horns and tusks). In this case, the lab-grown horns and tusks should be made indistinguishable from animal-derived ones and inserted into the illegal supply chain covertly. The dealers on the black market are not too honest people and would probably be happy to lie to their customers that lab-grown products are from wild animals.