You can try what I did - approach a track maker with your idea. If and when he says yes to your idea, be prepared to help out a lot, though. If the track has a website, that's a good start, but the track maker is going to need help with figuring out the layout, the degree of banking, etc. Then he's going to need lots, and I mean lots, of photos from all different angles and directions.
Probably most importantly, you are going to need patience. The Rushmore Scenic Byway track that I've been helping on has taken 15 months at this point. I've done a lot of photography, research and Photoshop work to help out, but I'm not the main track builder, just an assistant. I created the horizon background scenery from my photography, but the layout of the track, the elevation changes in the terrain, and placement of trees and other trackside objects is beyond my skill.
Or of course, you can get the Sandbox software and start on it yourself.
