I have one made by Kevin Gerlock. I don’t know if he still makes them or not but he used to be on TradGang with the handle ‘cupcake’. I used it the most when I was making and selling shafts and I have spine tested literally thousands of Poplar and Hickory shafts with it. I also have a Don Adams and one that I made with an aluminum frame and dial indicator. I use my home made one to cross reference the others.
I’m with Dennis, I believe the spine tester Kevin makes is the king of the heap. They are still for sale, they are called the Spine-O-Meter Mark II, do a google search you’ll find them.