TSTO Christmas Keys to SUCCESS!

I apologize if this was covered somewhere on the board, but I'm wondering what triggers a gift card to be available on my buildings when my neighbors stop by? Sometimes when I am visiting neighbors, i have to hunt and hunt to find a building with a gift card. Are they on the buildings which I have NOT yet tapped on? Does it benefit my neighbors if I am not as diligent at tapping on my buildings so that more gift cards are available? Can someone with two towns investigate this?

Thanks!