While there are still ways to buy LEGO sets that have long been retired, your best bet is to pick them up while they are still available at major retailers and haven't been marked-up by resellers.

In order to keep the bricky appearance of the train engine intact, [Robert] hollowed out a few cheap imitation LEGO bricks to house the electronics. He also cut out slots for JST connectors ...

The set in question is the LEGO Harry Potter Hogwarts Express & Hogsmeade Station Train Set ... is a great time to buy it thanks to Target’s discount.