Quoted By:
Assuming you wanted to be able to trade with yourself and transfer up pokemon from older generations to make the process of completing each game's dex easier, you'd need a GBA console with a GBA and a GB link cable, a GameCube with a Game Boy Player (some gen 3 mons are exclusive to colosseum and Gale of Darkness like Ho-oh and Lugia and having the game boy player means you won't have to have an extra game boy) a DS lite or Original so you can transfer from Gen 3 to 4, two 3DS consoles to allow trades between gens 4 and 5, transfers from gens 4 to 5 and 5 to 6, and trades between gens 6 and 7 and transfers from gen 6 to 7. Finally, you'll need a mobile phone and 2 Nintendo switches to allow trades between LGPE, gen 8 games, and transfers from gen 7 to 8 and gen 8 to gen 8(since BDSP can't trade with Sword and Shield for whatever reason)
If you really wanted the expired event pokenon, you have some options as well. The DS has fan servers up that have all of the past events for Gens 4 and 5 going on concurrently as well as other events that didn't exist for features like the azure flute or the unobtainable poketch apps or weren't available publicly like the world championship ones that only require you change the primary DNS in your wifi settings to access. Note that Generation 4 cannot connect to any network that has anything other than WEP encryption or none at all. Some Generation 3 event carts have been dumped on the internet, so if you want, you can buy a microSD, a flash cart, and 2 GBA wireless adapters and be able to use the carts as they were used during the actual distributions (I understand you want to avoid emulation and other illegitimate means of obtaining pokemon and games but using the flash cart is your only option for Generation 3 Events so do with that information what you will) Events from Generation 6 onwards though I believe are lost to time at the moment until the AltWFC community catches up.
