Adding another piece to create more variations on touch

In 1975 I used 2 broken Walkie-Talkies and conected them to my dad's amplifier. I spent hours making synth sounds. There is a catch, and I am unable to find anywhere. Those Talkies had a piece of about 12 cm with spikes, 2 rows. Depending on where I placed my fingers I had a diferent sound. Like your Playtronica. The Main Diference!! The preasure on the spikes created some form of a keyboard. Very rudimentary. Keyboard is not right, but the tones would change adding another dimension to the playing. I wish I could explain better. I would love to be able to add it to the Playtronica as a glove or something to hold...