Retro AI Traffic Group: https://retroai.proboards.com/
An immense storehouse of retro/classic AI traffic, spanning from the late 1940s to early 2000s. Many very talented artists showcase their work on this forum, and have links to their own remote drives for easy acess. There are easily several thousand available flightplans spanning this time period for all manner of airlines.
Mikey's Retro FS Corner 