You have to defeat Koga or the Ghost tower, I think.
in saffron city after you defeat team rocket
You have to beat team rocket in Silph Co
Go to Saffron City and beat Team Rocket in The Silph Co. Building
in saffron city but make sure that the team rocket grunt is sleeping
Saffron city.
Saffron City.
Saffron city.
Saffron city.
Saffron city.
Saffron City
Saffron city.
The card key is found on the 5th floor inside the Silph Co building in Saffron City you will need to get past a Rocket Grunt to get it.