The reason for this is most people who would fix it would scrounge up the pieces if needed to do the repair, but they're not going to go scrounging up pieces just to sell them to someone, that's way too much work for what the part alone would be worth, not to mention that the part in question may not be the cause, so they can go further if necessary to get the right solution. If you're willing to pay a rather perverse price for a piece that may or may not fix your problem, I'm sure you can find someone that can scrounge one up for you, but you would have to be willing to accept all the risk of installing the part and accepting that the part itself may not be the solution to your problem.