It's not that hard to make one. There are plans available using a dial indicator, etc. I made one where the frame was made on a 3D printer. You can calibrate it using weights or a spring gage like in the photo.
Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit HomebuiltHelp.com for the latest DVD titles.