All you need is a block of wood, a drill driver with 4mm drill bit, a counter sink, sandpaper bit and a way of clamping the wood down. Took me about 15-20 minutes.
Firstly mark out where the darts will sit in the block of wood, I did this using the darts themselves and making an imprint in the wood with them when I was happy with the spacing.
Once this is done, using the drill make the holes in the wood. I suggest making the holes 6-7mm longer than the dart tip so that the tip doesn't rest on the wood. When the holes are drilled you can countersink them so that the darts sit better in the holes so that the barrel is well supported. Finally you can sand down the block to give it a tidy finish