Well, 1:1 endo arms pop up from time to time on eBay, but I suspect they are recasts of the Timeless collectibles or Sideshow arm. These usually come from China, and that's the first tip-off that they are recasts.
Can you make one? I suppose so, if you have measurements, that depends on your skills and choice of materials. Most of it can be made from PVC pipe and other bits found at most hardware stores. It might not be 100% accurate, but it will be close.