The border block, Command block, allow block, and Deny block cannot be gotten from the creative inventory.
They can only be gotten using a command. /Give.
If you want to use the border block, a block that blocks all member players from going out of the perimeter, you need to do /give @s border_block That’s how you do it. When you do that, it will automatically give you a border block, use it as a say, and you can block people from going out of the perimeter.
However, you can also get through it using boats. So, you need to use at least 2 layers.
