It's very easy to make a range rod! Here's how I do it.
First, get the rod itself. You can use hardware store brass, steel, stainless steel or plated steel. They all work. You could also use fiberglass or delrin. There's probably a few others to boot.
The diameter of the rod is determined by the caliber of the rifle(s) it will be used with. A 5/16" covers .45 to .58 for example.
The other things you need are something for a handle. A few things I have used are antique door knobs, hardwood balls, pool balls, dowel wood, and file handles. A bore guide with an ID to match your rod. A ramrod tip with an OD 1/16" larger than the rod (eg., 5/16" rod, 3/8" ramrod tip). The 5/16" rod will fit into the ramrod tip.
So epoxy and pin the rod into the handle. You will probably need to drill the handle to 5/16" and then drill a smaller hole crossways through the handle and the rod. Then epoxy the rod with the pin into the handle.
When the handle glue is cured slide the bore guide onto the rod and then epoxy and pin it same as with the handle. The rod tip will capture the bore guide.
Done. Screw whatever size jag you need into the tip and sheeeezammm. Range Rod.