You cant it already has one.
its only on april fools day but here's a code to get a free pumpkin its "PUMPKIN1"
its free for everyone when its April fools day just throw paint at snow forts or dock then you have it
you can get it at the Festival of Flight. but the Festival of Flight is over, so you will have to wait until the next one, but if it's not coming back, you're out of luck.
It is in the April catalog in the Gift Shop.