This assumes you have a press, screw, hydraulic or rack.
Take a piece of cold rolled steel. Support it on two pieces of round stock a known distance apart. The round stock will have to be blocked up a few inches because space is needed underneath the center of the cold rolled.
Now you have a simply supported beam for which you can easily determine
I and can make a plot of beam deflection versus load.
Mount a dial gauge under the center of this beam; apply pressure from the press; again via a piece of round stock at the center. Now you can relate deflection of the beam to the force being applied by the press.
If it is a hydraulic press it should have a gauge; you can now calibrate the gauge in terms of force applied by the press. If it is a screw press you will need to use a torque wrench and if it is a rack driven press you just need a spring scale between you and the end of the lever.
You will need to choose the dimensions of the cold rold and the distance between the supports to get the calibration rig somewhere close to the range you want to measure. Just remember you have to be in the elastic region during calibration. If the dial gauge does not return to zero when the force is removed you have move into plastic deformation.
EDIT; Obviously I was reading Yugami's mind, or vice versa.