Where do you find the third pass in Pokemon fire red?

You don't find a "third pass" in Pokemon FireRed. You are likely thinking of the "S.S. Anne Pass", which is a key item used to access the S.S. Anne. You get this pass from the Captain on the S.S. Anne after you complete a short puzzle with him.

Here's the breakdown:

* Where to Find the Pass: You need to talk to the Captain on the S.S. Anne after you board the ship. He'll ask you to help him find his daughter, then lead you through a simple puzzle.

* Getting to the S.S. Anne: To reach the S.S. Anne, you need to travel to Vermilion City and head to the port. The ship will be docked there.

Let me know if you have any other questions about Pokemon FireRed!