How can I create an artificial corrupted desert biome?

Dark Mummies spawn on Ebonsand blocks in the Corruption, and that's about it.

What I did was build a long strip of Ebonsand in the sky, and then I ran back and forth with a Battle Potion active. You can also coat an area in the Corruption with a 1-block layer of Ebonsand so that every monster spawn has a chance to be a Dark Mummy.

If you have a Steampunker living in one of your houses, then, buy a clentaminator from her. During a blood moon, she will sell purple solution for the clentaminator. Buy it and spray it where you want, and it will create corruption wherever you spray it.

You need to farm some corrupted ebon stone from the underground hard mode corruption biome. I'm pretty sure one brick will do it, though more might speed up the process. Anyway, go place the brick or bricks in the desert. Just make sure they are touching the sand. Eventually the corruption will spread into the desert, and you have your corrupted biome.