Instructables user Jazzmyn has designed her own pieces for a marble machine. They’re pretty basic parts, curves, switches, and Ys. But they all connect together and in whatever way you want to combine them. You can download the parts on Thingverse, but you will obviously need a 3D printer in order to build your own.
Here’s a video of the finished machine. It’s pretty nice, but there is some room for improvement in future