This is a simple bracket that allows you to insert pre-cut hardwood strips from your local hardware store or home center.
The opening are sized to fit 1/4"x2-5" pieces which you can get in various lengths. The ones I used were 24" poplar and they cost me about $1.20 US
If you want it to look a bit nicer, you can use oak and stain it.
The fit should be snug, so a rubber mallet may need to be used to tap the brackets on.