Steve,

They are usually available at the sportsman's shows however, they are very easy to make.
Just buy either a 1/2" or 3/4" wooden dowel and some cabinet cup holders and screw into one end. Done! They are also handy for various other things like grabbing the release instead of leaning over the boat. Again, I mark off the 22" mark for a quick reference for fish. I also have one inch increments marked off...