Dark Eldar build "replica" of golden throne. They could trade it with Trazyn for multiple STC and then trade it with mechanicus. First question how many humans would mechanicus be willing to sell for a single STC? Second question how long will it take for Trazyn to want to get Emperor to have a full collection? And if your answer is not "immediately after getting throne" or "he already wants" then it's wrong.
source for the necron picture?