Where is the guy that trades Abra at Pokemon FireRed?

The guy who trades Abra in Pokemon FireRed is found in Fuchsia City, specifically at the Game Corner on the second floor. He's standing by the table with two other people, and he'll trade you his Abra for your Kadabra.

Keep in mind you need to have traded your Kadabra for an Alakazam and then traded it back to get it back. You can do this with someone else if you don't have two players.