PowerA Controller Replacement Parts?

I have a wired mini PowerA controller but the buttons (square, triangle, etc) aren't as responsive or don't give the same feedback because the silicone padding for the buttons (when you press down) are really worn down. I can't for the life if me find any replacement parts for the button padding, and don't want to buy a new one. Any ideas where to buy them?

It's a mini so normal ps3/4 or Xbox pads do not work.