Hello I will help you with your question,
If you can find one used that would be the way I would go but it might be difficult to locate one. Car-part.com or LKQ.com will show most of the wrecking yards in the country but this is not the sort of part that survives to make it to the recycler.
If you have have the oil changed or other service I would stop by to inquire if the undercover was left off and might be stuffed behind a toolbox waiting for your return. It happens more often than it should
This is listed as a noise insulation panel
Maybe check the service department of your dealer or their bodyshop, there might be one sitting around.
Let me know how I can be of help