The connectors (USB and Audio jack) are standard PCB-mounted jacks, so you should be able to find them on ebay etc.

The potentiometers also seemd to be standard parts, so you should be able to get those quite easily as well

Try searching on e.g. ebay for “3 pin pcb mount female 3.5mm jack”

The plug is a standard part, so it should be readily available. I replaced my plug with a scavanged part that I happened to have on hand!

I had some problems removing the buttons with my fingers (they were too slippery). I got them off quite easily using a pair of adjustable pliers / multi-grip pliers.

The buttons are the standard friction-fit potentiometer buttons, so it shouldn’t take too much force to remove them