Here's the factory transfer case skid plate installed on the car (along with the factory gas tank skid plate on the right)
If you're going to do this, remember to let the screws create the threads in the frame holes instead of tapping. If you tap the threads, the holes will be too weak and will strip out (I know from experience)
Transfer case skid plate install:
1x - 6L2Z-7E063-AA - Transfer case skid plate ~$100
4x - W707079-S439 - M8 Thread forming washer bolts ~$5
Gas tank skid plate (bonus):
1x - 6L2Z-9A147-AA - Gas tank skid plate (plastic) ~$300
1x - 1L2Z-9A235-AA - Skid plate support bracket (discontinued so you'll have to fab your own)
4x - W505444-S439 - M10 washer bolts (same used on the bumper)
4x - W710792-S439 - M10 Insert Nut (same used on the bumper)
1x - W712295-S439 - M10 Insert stud (same one used on the front fuel tank strap)
1x - M10 flange nut
FYI - Having done all the work of buying and installing these, I'm not sure I'd do it again. The gas tank skid plate is 1/4" thick, but it's still plastic, so I don't know how much I trust it. The transfer case skid plate doesn't seem like it's worth the metal it's made out of. I think it would need a center support (as Bazz270 mentioned) to be of any protective value.