you can get the gold key card in the scrub-e game,
but it's a couples game so make sure you have hamtaro too.

after the two by the elevator help you get hamtaro out
of that steel cage thing, they'll be back at the elevator.
talk to the one pushing the elevator, he'll say they
need a care key, and the bigger one will say he's right.
then they'll leave and you can use the gold key to get
in the elevator :]