If you go to the ruins where you can find Unknown and you use Rock Smash on the rocks, there's a slight chance that you'll find a fossil. The Aerodactyl fossil is the Old Amber, and the Omanyte fossil is the Helix Fossil. You'll probably have to keep using Rock Smash for awhile before you find a fossil. Then you go to Goldenrod and take the Magnet Train to Kanto. Once in Kanto, go to Pewter City, and go in the museum. Talk to the guy at the right side of the building and he'll revive the fossils for you. Or, of course, you can trade somebody. Hope this helps!