How is a 'ribbon controller' called in electrical terms?
The most basic ribbon controller is a linear potentiometer, or a resistive touch sensor. Your finger sets the wiper position. It might be easier to do it with a linear capacitive touch sensor and microcontroller. I'm not aware of commercially-available pots in this form factor. 

More advanced controllers also have integrated force sensors, similar to those you find in synth pads, that respond separately to the linear sensor. You will have to find a way to assemble the two sensors yourself. (Maybe a stack like capacitive touch sensor pcb/rubber/pressure sensor).