I used a tension gig to calibrate the sensors in the project, which are swinging pots. Then the swinging pots do the job. If I understand correctly you are looking for something to move around the path.
Here is a tool that may do the job for up to 50mm ribbon.
@npiegdon had good results working with a load cell.
A 3 roller design as shown in the tension meter in the link, where the center roller is mounted in a load cell should do what you are looking for. Although one limitation would be that the range of the sensor would be limited by the range of the load cell.
Last option, there is always an arm, a pot, and a spring. The center roller (instead of a loadcell) may be the arm tensioned by a spring and measured by a pot.