A panhard rod (aka track bar) is not a complicated device, so yes you can fabricate one. Just make sure it is shaped right so that it clears the rest of the suspension over the full length of its travel. If you aren't careful, it will hit something when the suspension compresses all the way. And of course, it needs to be rugged & strong.
There are videos and "How To" instructions available online. Here are a couple of them: