What PC do you go to get the Aurora ticket in firered?

You don't get the Aurora Ticket from a PC in FireRed. You actually get it from Professor Oak in Pallet Town after you've defeated the Elite Four and become the Champion.

Here's a breakdown:

1. Beat the Elite Four and become the Champion of the Kanto region.

2. Return to Pallet Town and talk to Professor Oak.

3. Oak will congratulate you and give you the Aurora Ticket as a reward for your achievement.

This ticket allows you to travel on the S.S. Anne to the Sevii Islands, a post-game area filled with new challenges and Pokemon.