Where can you get the skull fossil and armor in Pokemon black?

You can't get a skull fossil or armor in Pokemon Black. Those are items from Pokemon White and are used to revive Archeops and Tirtouga respectively.

In Pokemon Black, you can find the cover fossil which is used to revive Kabuto and Omanyte and the jaw fossil which is used to revive Cranidos and Shieldon.

These fossils can be found at the following locations:

* Cover Fossil: Located on Route 16, inside the Fossil Mania shop

* Jaw Fossil: Located inside the Fossil Mania shop, which is available after you defeat the Elite Four.