I've made cork dart & knife throwing boards before for scouts, it's not terribly hard constructing them. Just cut a 3/8 or 1/2 inch plywood backer in the shape you want and order some 1/2 - 1 inch thick sheets of cork from amazon. 3M super duty spray adhesive the 2 together, best if you have some spare plywood that you can put on top and put some weights on it for a day or two to really press the 2 together especially if they were rolled or bent in the box. Then trim the excess off.
The trick is painting with the water based acrylic latex. It's what I had found the best as it stays flexible and self heals the best when the dart/knife is removed. The cork can swell from the moisture in the paint. Have to lightly airbrush it or cross your fingers you can get a really light rolled/brush coat of your base color or Kilz water based latex primer and the cork not do something funky.
If you can live with the brown base color of the cork, permanent sharpie markers work pretty good too.