Anyone know where I can get that back board/poster thing to go in the back of the easter basket??…

Anyone know where I can get that back board/poster thing to go in the back of the easter basket?? I'm making my son, niece and nephews Easter Baskets this year and bought alot of candy and toys to go in it and my baskets are little so it doesn't fit everything. Need the poster cardboard thing to tape some of the stuff on.