This is becoming more and more of a problem as everything becomes more complex. I remember when I was a child my dad repaired the power switch on the vacume cleaner by going to the local electrical store and buying the exact same switch. Now every single device has its own custom part and the switch isn't just connecting 2 wires, it's contacting a main board telling it the button has been pressed triggering the power…
The good news is you can get almost anything on the Internet. I've found so many weird parts from shady eBay sellers that worked perfectly in the end. Other times I've had to order a similar part off of Mouser and hack it to make it fit, with varying levels of success.
I have had a surprising amount of luck with some items though. Managed to replace the shoulder buttons on my 3ds by finding a replica of the button + ribbon cable + connector used.