Someone asked me if there was a motor spring tension gauge for sale. Here is a link to the Spring Thing by Trinity. It may not read in ounces, but it will let you reproduce spring tensions.
http://www.teamtrinity.com/motors/motor_tools2.html
There is no reason you could not push this device on a postal scale and put marks on it to calibrate it in ounces. The only advantage here is the ability to compare data with someone else.