Where can I buy older sets that are not in stores any more?
Easiest place to find them is at public auction sites, but you will pay top dollar and you need to be careful to get a good description from the seller so you know what you’re getting. If the set is used there may be pieces missing or pieces substituted. Sometimes you can find older sets in smaller independent toystores, or used ones at garage sales or via classified ads. You can also check Bricklink, where people sell sets as well as parts, or ask on LUGNET or rec.toys.lego. There’s no easy way: you just have to keep looking.