The people who have 5000 of something typically found a case in the store that the live very close to and that they visit frequently. This includes the stores within LEGOLAND amusement parks. (I have heard that you can get a two hour pass to go shop the store in the park for free, but I have never been to one of the parks, so I don’t know firsthand.) Your best bet would be to try to get a bulk deal with someone who found a whole case of the part you want or to try calling the stores directly if you have an idea where the parts came from. For example, if the parts suddenly show up in a bricklink store of a person living in NC, call the LEGO store in NC. That’s my $0.02. 🙂