Where can you find fossil claw in sapphire version?

You cannot find a Fossil Claw in Pokémon Sapphire. It is a specific item introduced in Pokémon Diamond, Pearl, and Platinum and is not available in earlier generations of the game.

If you're looking for a way to evolve your Pokémon that requires the Fossil Claw, you'll need to trade for one from a player who owns a game from Generation IV or later.