Where is the best way to purchase legitimately an older version of flight simulator (4.0 or less)?

Aren’t really old versions available on myabandonware? Not sure what the copyright implications are there - up to the user to decide (for instance, I own the software, but the disks are unusable). Hook ‘em up to DOSBox and away you go! I did this just before the Easter egg was released in MSFS. It was very nostalgic.