match-3 Board border

Hi,

I'm new to unity and I'm currently working on a match-3 game.
I know there are a lot of similar games and that's why I would like to know what is the best way to autogenerate border of a match-3 board game ?
Till now I have tile with game pieces but I would like to make unity to autogenerate (select from a pack of images/sprites) board borders as you can see on the image below (it is an example):

My board is not necessary a rectangle or a square and its size is generated from the inspector of "board" game object.

thanks a lot.