Re: (PvZ GW1 - PS4) How do I obtain these stickers?

Hi, these items appear to be part of the Trick or Treat event, and they were only available temporarily. 

You can find more details about the event here: http://plantsvszombies.wikia.com/wiki/Trick_or_Treat_event

Sorry that we can't help with getting the content, but I hope this helps. 

Cheers.