#1 source for all bits and pieces McIntosh: https://www.audioclassics.com
Ryan Kilpatrick is the go-to guy for parts there. If anyone has them, they will.
BTW, you say an electrostatic cleaner? I'm not 100% sure, but I believe most plated knobs are electro-plated. If so, you likely broke the ionic bonds between the plating material and the knob surface. The knobs would have to be re-plated.