There are a ton of examples of such blocking boards for sale on Etsy. My sister pointed me to a couple of them, but this was the example she sent. She thought they were a little expensive, especially for the size, and was hoping I'd make her a little bigger one. I, of course, went overboard and initially designed and laid out a 24" square board, but . . . 

1. It was too big for her to work with
2. She had flown down from Ohio to Georgia to attend DragonCon, and I was planning to give it to her then, But there was no way she could fit a 2' square board anywhere in her luggage.

So I cut it down to 18" square, which . . THANK GOD!   Because if I had gone ahead with my plan for a 1/2" on center grid of holes at 24" square, I'd still be drilling holes a month later.

As it was, I did go with the half-inch on center hole grid. I gave myself an inch and a half border, but that still resulted in a 31 x 31 grid.   Yes, I drilled 961 holes.   Those Etsy blocking board don't seem that overly expensive to me anymore.