This article explains the different ways you can get rare gold stickers when playing Monopoly Go.

Stickers offer additional opportunities to earn in-game rewards, provided you complete a set. Gold stickers are the rarest and hardest to find. Completing a particular sticker set usually grants additional dice rolls and money, but some also contain tokens that you can use to represent yourself on the game board.

If you want those gold stickers and can't wait, the fastest and easiest way to fill your album is to pay for them.

On the main screen, tap the shop icon (it looks like a stall) in the top left corner.