In the US here we can obtain strut from Home depot or Lowes in the electrical department. Also electrical supply houses will carry strut. Strut comes in a few sizes, shallow strut and the strut we need. The strut we need is 1-5/8" X 1-5/8" X 10 ft. The electrical supply houses will have it in 20ft lengths so it will need to be cut down.
Our metric friends will need 41mm X 41mm strut and fits just fine. We imagine that electrical supply places will have the strut. We have sold many jigs around the world and everyone has been able to find the strut. If you need help we can put the word out in a country near your location.
For the length I would like to add a note. There is a few bows around that require a little longer than a 10ft strut. Solo cam Mathews Conquest has about a 113" string, With the strut being 120" and the jigs take up some room an extra 10" of strut can come in handy. Some folks will flip the stretching post around to gain some length while twisting the string.