after you beat brock and go through the cave you pick one fossil you cant get the other unless you trade so pick carefully
it depends what year the action replay is
To help Lorelei in Pokemon Firered, you must travel to Four island (Floe island) and enter the Ice Cave. Work your way through the maze-like obsticles and you should find Lorelei in a room with mostly water. She will tell you what to do from there.
Go to the right side of Route 2 (need HM01 Cut) and in one of the buildings there should be a man who will trade you a Mr. Mime for an Abra.
you can find Abra on Routes 24 and 25, and can buy one at the Celadon Rocket game Corner for 120 coins.
Under normal circumstances, Mew is un-catchable during normal game play. If you did the Nintendo Events a few years back, you'd get an Aurora Ticket that would take you to Birth Island where you can catch Mew. Unfortunately, those events are long over. The only ways to get Mew now, is to either: Trade from someone who has one, or use a cheating device to automatically encounter Mew, or hack him into your party/box. Keep in mind, if you use cheats, Mew will not obey, regardless of badges earned. But at least you can get the Pokedex entry.