PTCG Archive is a fantastic resource kept by Ben Robinson that details decks for many different years, as well as detailed pages for tournament results, player rankings, and more.
Jason Klaczynski’s Retro Deck Blog:
Jason Klaczynski is a 3-time pokemon world champion. Since retiring from competitive play, he has made it a goal of his to give fantastic insight into the history of the game, how the metagame devoloped, and providing decklists for many different eras.
Jimmy Ballard was another phenomenal PTCG player, and today, TOs some of the most prominent events in the country. He placed 2nd at Worlds in 2006, and is referenced several times in the retro deck section here for high placements with decks that were often quite unique. His website has many decklists put together spanning between 2003 and 2012, all of them with links to ProxyCroak for easy printing of proxies.
Snowpoint Temple Facebook Group:
An active facebook group that discusses old formats and even hosts tournaments! There is also a secondary group – Snowpoint Mart – where you can buy cards for retro decks from other like-minded individuals.
Jay Hornung was a player from the midwest who consistently placed highly at tournaments. He has started a youtube channel and provides extremely valuable insight in decklists, and is one of the few players today who pushes to create his own ideas, even years after the formats are completed. Jay also has a twitter dedicated exclusively to pokemon content, which can be found here.
Run by Drew Allen, this youtube has deck profiles for many decks of many different years, and also has a short introduction to the entire concept of “retro formats”.
PTCG Legends is run by Alex Wilson and documents decks from basically every era of the TCG, as well as tournament results! Not only does this website document results from retro eras of pokemon, but it also features results from today’s events, and is constantly updated with new decklists and results. There are also pages for 1st turn rules, expansions with set symbols & abbreviations, Japanese tournaments, and more! Definitely give this website a look!
ProxyCroak is probably the easiest way to print Proxies for retro decks in the TCG. Make sure you put the pokemon set abbreviation and collector #, and also make sure “legacy support” is turned ON when printing ex-era decks.